Block Definition and 998 Threads

A block of the periodic table is a set of elements unified by the orbitals their valence electrons or vacancies lie in. The term appears to have been first used by Charles Janet. Each block is named after its characteristic orbital: s-block, p-block, d-block, and f-block.
The block names (s, p, d, and f) are derived from the spectroscopic notation for the value of an electron's azimuthal quantum number: sharp (0), principal (1), diffuse (2), or fundamental (3). Succeeding notations proceed in alphabetical order, as g, h, etc.

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  1. C

    Finding the mass of a block after colliding with a spring

    Homework Statement A block moves along a frictionless surface with an initial velocity of 10 m/s. It contacts a spring of spring constant 350 N/m. Underneath the spring at and after the point of contact the ground is rough and applies a constant friction force of 45 N. The spring compresses...
  2. D

    MHB Block diagrams from state matrices

    How does one construct a block diagram from the state space representation? Consider the state space: \begin{align} \dot{\mathbf{x}} &= \begin{pmatrix} 0 & 1\\ 0 & 0 \end{pmatrix} \mathbf{x}(t) + \begin{pmatrix} 0\\ 1 \end{pmatrix}\mathbf{u}(t)\\ y(t) &= x_1(t) \end{align}
  3. S

    Block Sliding Down Inclined Plane with Pulley and Friction

    Homework Statement A block with mass m = 5.00kg slides down a surface inclined 36.9 ∘ to the horizontal (the figure (Figure 1) ). The coefficient of kinetic friction is 0.27. A string attached to the block is wrapped around a flywheel on a fixed axis at O. The flywheel has mass 23.0kg and...
  4. G

    Find angular velocity given velocity of attached block

    Homework Statement The block at C is moving downward at vc = 4.8 ft/s. Determine the angular velocity of bar AB at the instant shown. Homework Equations x = cross product r = distance to point from frame of reference Boldface will indicate vectors v = ω x r vB = vA + ω x rB/A =...
  5. K

    A block on a frictionless circular ramp

    1. The problem statement, ramp. variables and given/known data A block with mass m=5kg is placed at position A and given an initial velocity Va=2m/s Down a frictionless circular ramp. Between positions B and C it travels over a flat rough surface having a coefficient of kinetic friction...
  6. R

    Speed difference in the pulleys in a block and tackle setup

    I am designing a block and tackle system (because I can't think of anything more simple) to take up the slack in a loop of cordage for a machine I am tinkering on. The loop only travels in one direction due to a set of cam cleats. I am trying to figure out if all the pulleys in a block need...
  7. T

    Buoyancy, depth a block will sink in two different liquids

    Homework Statement 4. The bottom half of a tank is filled with water (ρ = 1.0 x 103 kg/m3), and the top half is filled with oil (ρ = 0.85 x 103 kg/m3). Suppose that a rectangular block of wood of mass 5.5 kg, 30 cm long, 20 cm wide and 10 cm high is placed in this tank. How deep will the...
  8. K

    Instrumentation amplifier: why subtractor block?

    Hi, I'm looking at a circuit of a classical instrumental amplifier having 3 opamps, 2 for buffer, with Rg to adjust the gain. The output from this buffer + gain circuit is then feed into a third opamp, in a circuit that is the 'basic' differential amplifier, but whose function now that Rg is...
  9. D

    MHB Bullet imbedding in a block on a frictionless surface

    A 10g bullet with v = 1000 m/s strikes a 100g block which is at rest. What is their combined velocity? Can this be done with conservation of energy? momemtum? Here we have inelastic collision so by conservation of momentum \[ 10\cdot 1000 + 0 = 110\cdot v_f\Rightarrow v_f =...
  10. S

    Forces - A block slides upward on a rough, vertical wall

    forces -- A block slides upward on a rough, vertical wall Homework Statement A block slides upward on a rough, vertical wall at constant velocity when a force F of 60 N acts on it at an angle Ɵ = 60ᵒ to the horizontal. The mass of the block is 3.0 kg. See picture below. a) Using...
  11. D

    Block diagrams to transfer functions

    Homework Statement I am trying to write a block diagram as a transfer function. Homework Equations The Attempt at a Solution Let ##G = \frac{1}{s}##, ##H = \frac{K}{Js + a}##, and ##L= K_f##. Then wouldn't the closed loop transfer function be written as $$...
  12. danjordan

    Block floating in between oil and water, what's the FBD?

    [Mentor note: This thread was moved from General Physics due to it being homework related] A friend and I were reviewing problems from a GRE subject which read: "A layer of oil with density 800 kg/m^3 floats on top of a volume of water with density 1000 kg/m^3. A block floats at the oil-water...
  13. jbunniii

    Kleppner - Block on wedge with friction

    Homework Statement This is problem 2.17 from Kleppner and Kolenkow, 2nd edition. It is the first problem involving friction, and I want to check my reasoning. A block rests on a wedge on a horizontal surface. The coefficient of friction of the block on the wedge is ##\mu##. Gravity is directed...
  14. D

    Bullet striking a block on a frictionless surface

    Homework Statement A 10g bullet with velocity 1000m/s strikes a 100g block at rest. What is their combined velocity? Can you work the problem with conservation of momentum? Energy? Homework Equations The Attempt at a Solution For conservation of momentum, we have $$ 10g\cdot...
  15. K

    Block-on-Block attached by String to Block in Pulley on Incline

    Hi all, The problem is shown below - but no answer was given to this, and the teacher did not plan on taking it up, since it was optional extra practice. My attempt at a solution: http://imgur.com/DmrgMMO, my final answer was 2.76 kg. I was wondering if this was right or wrong, and if...
  16. KiNGGeexD

    Buoyancy - block of concrete is being raised from a lake

    Buoyancy -- block of concrete is being raised from a lake Question; A 50kg block of concrete is being raised from a lake. What fraction of its weight in air is required to lift it while submerged? My attempt, I'm pretty sure this question pertains to Archimedes principle I calculated the...
  17. A

    Time Question - how long did the train block the crossing?

    Time Question -- how long did the train block the crossing? Homework Statement A commuter train 500 m long travels on a straight track at a speed of 78.6 km/h it slows down as it approaches a crossing. The last car passes the crossing at a speed of 15.8 km/h. With a constant acceleration, how...
  18. jbunniii

    Block sliding on accelerating wedge

    Homework Statement This is problem 2.11 from Kleppner and Kolenkow, 2nd edition. I have completed the problem but I'm not 100% sure I did it right and would like to check my understanding. A ##45## degree wedge is pushed along a table with constant acceleration ##A##. A block of mass ##m##...
  19. T

    Initial acceleration of block when string is cut

    Homework Statement In figure shown, pulleys are ideal m1 > 2 m2. Initially the system is in equilibrium and string connecting m2 to rigid support below is cut. Find the initial acceleration of m2? Homework Equations The Attempt at a Solution In equilibrium, 2T1 = T2 For...
  20. S

    Can aluminum foil block the sun's UVA rays?

    Hello everyone. I was just curious if aluminum foil could block the sun's UVA rays. I have my home office and the sun always gets in and hits me. I know sunlight can cause early photoaging and cancers, so I want to block out as much UVA rays as possible. I do wear sunscreen, but I prefer...
  21. G

    Work Done on a Block on an Inclined Plane

    Homework Statement A block of mass m=18kg is pushed horizontally with a force of Fp=150N up an inclined plane of angle θ=32° and coefficient of friction of μ=0.10, a distance of x=5m. a) What is the work done by Fp. b) Work done by the gravitational force. c) Work done by the normal force...
  22. I

    Sliding block with motion restricted by spring

    Restricted Block on Spring A block of mass m = 2 kg slides back and forth on a frictionless horizontal track. It is attached to a spring with a relaxed length of L = 4 m and a spring constant k = 8 N/m. The spring is initially vertical, which is its the relaxed postion but then the block is...
  23. A

    Acceleration of a block with static & kinetic friction

    A 10kg block is at rest on the floor, and then a force of 30 N pushes on the block horizontally. If the coefficient of static friction between the block and the floor is μs= 0.33 and the coefficient of kinetic friction between the block and the floor is μk= 0.20, what is the acceleration of the...
  24. P

    Displacement of Oscillating Block: y=A cos(ωt+ø)

    A block of 5kg connected to the free end of a spring is hanging from the ceiling and is in SHM. At t=0, the block is traveling upwards and its displacement is 15cm from the equilibrium. The block reaches its maximum displacement 0.3s later. What is the general equation of the displacement of the...
  25. G

    Finding the Transferred Energy for a Block Sliding Down a Ramp

    Homework Statement A 5.0kg block slides down a ramp, starting with a velocity down the slope of 2.5 m/s. The ramp is 1.5 m high and has an angle of 25 degrees. The force of friction acting upon the block is 20.0 N. How much energy is transferred in or out by gravity, normal force, and...
  26. B

    Falling Block Pulling Rolling Cylinder

    Homework Statement A uniform, solid cylinder of mass M = 4.22 kg and radius R = 0.36 m with I=1/2(M*R^2) is attached at its axle to a string. The string is wrapped around a small frictionless pulley (I=0) and is attached to a hanging block of mass 1.69 kg. You release the objects from rest...
  27. S

    MHB Eigenvalue separation of a Block Matrix with a special structure

    Hi everyone, I have a square matrix J \in \mathbb{C}^{2n \times 2n} where, $J=\left(\begin{array}{cc}A&B\\\bar{B}&\bar{A}\end{array}\right)$ A \in \mathbb{C}^{n \times n} and its conjugate \bar{A} are diagonal.Assume the submatrices A,B \in \mathbb{C}^{n \times n} are constructed in a way...
  28. A

    Ear muffs that block human speech?

    Apparently, from what I heard, it's illegal in the US to sell headsets that block sound in the 1k Hz to 2k Hz frequency range. The problem is that human speech is in that range and I want to block human speech so I can study. Normally, the product description reads something like this...
  29. V

    Determinant of a Block Lower Triangular Matrix

    Homework Statement Theorem. Let A be a k by k matrix, let D have size n by n and let C have size n by k. Then det \left(\begin{array}{cc}A&0\\C&D\end{array}\right) = (det A)\cdot (det D). Proof. First show that \left(\begin{array}{cc}A&0\\0&I_{n}\end{array}\right) \cdot...
  30. soothsayer

    Can lead shielding block beta particles?

    I know lead is a great shield against gamma particles due to its extraordinary density, but I wonder if it can also block beta particles, or is it transparent to them due to being electrically conductive? Thanks ahead of time for your responses!
  31. D

    How Do You Calculate the 3dB Frequency for High and Low Pass Filters?

    Homework Statement (a) The input capacitor and the voltage divider network form another high pass filter. Calculate f3dB for the input high pass filter made with C = 4.7uF and the appropriate R value. (b) calculate the f3dB for the output pass filter made with C = 4.7uF and R = 100K...
  32. P

    Kinematics problem - Bullet in block of wood

    Homework Statement A 3.50kg block of wood is at rest on a 1.75-m high fencepost. When a 12.0g bullet is fired horizontally into the block, the block topples off the post and lands 1.25m away. What was the speed of the bullet immediately before the collision?The attempt at a solution d=1/2at^2...
  33. R

    Understanding Velocity in a Massless, Frictionless Pulley System

    Homework Statement Find V if the pulley is massless, friction less and Can take any no of variables but V is be in terms of VP.Ignore gravity and other forces 2. The attempt at a solution If Pulley comes down by X, the length of string towards left(the side not fixed) will increase by...
  34. P

    What is the effect of curvature on the rigidity of a beam?

    I didn't want to derail the last thread on the sliding block, but I think I noticed something interesting. If we look at http://arxiv.org/abs/0708.2490v1 consider first the image in figure 3 and compare it to the image in figure 11. Ignore the wheels, which complicate...
  35. A

    Block pushed up an incline, velocity using work

    this question has 4 parts, I am having trouble on the last part but i will post all parts to give context. Part A How much work is done by the horizontal force FP = 150 N on the 18-kg block of the figure(Figure 1) when the force pushes the block 5.5m up along the 32∘ incline? Assuming a...
  36. A

    How to find the the acceleration of the block M?

    1.Homework Statement Find the acceleration of the block of mass M in the situation shown.All surfaces are frictionless 2.The attempt at a solution 2Mg-2T=2Ma T=Mg-Ma and T-mgsin30=ma But a is canceled .what to do?
  37. P

    A block slides down an inclined plane of slope angle (theta)

    Homework Statement A block slides down an inclined plane of slope angle (theta) with constant velocity. It is then projected up the same plane with an initial speed v(knot). (a) How far up the incline will it move before coming to rest? (b) Will it slide down again? Homework...
  38. H

    Two block friction incline problem with rope

    Homework Statement Block A weighs 60N and rests on top of block B which weighs 80N and rests on an incline plane with angle of elevation 30 degrees. Block A is restrained by a mass-less rope as shown. What force F will cause block B to start moving down the plane? Assume all surfaces have a...
  39. J

    Newton's Laws - finding acceleration of block on sled

    Homework Statement A 4.0 kg toboggan rests on a frictionless icy surface, and a 2.0 kg block rests on top of the toboggan. The coefficient of static friction μs between the block and the surface of the toboggan is 0.58, whereas the kinetic friction coefficient is 0.48. The block is pulled by...
  40. C

    Understanding Tension in a Block and Tackle System

    Homework Statement The boy is lifting himself using the block and tackle shown. If the weight of the block and tackle is negligible, and the combined weight of the boy and the beam he is sitting on is 120 lb, what force does he have to exert on the rope to raise himself at a constant rate...
  41. H

    Critical angle (torque) at which the block tips over

    Homework Statement I know this tipping a block question has been asked many times and I know how to find the critical angle at which a block tips over. I was just wondering how one would go about analyzing the torque of the system. We all know that anywhere from 0 to the critical angle...
  42. Saitama

    How Is the Speed of Contact Point B Calculated in Rod and Block Dynamics?

    Homework Statement Rod AB is placed against a block which is moving towards right with a speed of 1m/s. If at an instant when the rod makes an angle ##60^{\circ}## with the horizontal and end A is sliding towards left with a speed of 1m/s. Then the speed of the point of contact B of the rod is...
  43. T

    Block Hitting Spring: Time to Travel x=0 to x1

    Homework Statement A small block of mass m=1 kg and v0=6.32m/s hits a massless relaxed spring with spring constant k= 3 N/m, which starts to be compressed as the block continues to move horizontally. There is friction between the block and the horizontal surface, and it is not uniform. As a...
  44. R

    RE:Newton's Laws of Motion Block Problem

    Homework Statement In the arrangement shown, all surfaces are frictionless, mass of block M = 30 kg and m = 20 kg. If F = 180 N , Find accelerations of both the blocks 2. Doubt How much force will be applied on the larger block M by the pulley(coz of tension)? 1. T towards right 2. T towards...
  45. R

    Newton's Laws of Motion : Block Problem

    Homework Statement In the arrangement shown, all surfaces are frictionless, mass of block M = 30 kg and m = 20 kg. If F = 180 N , Find accelerations of both the blocks 2. Doubt What amt of force will act on larger block M, just T(coz of horizontal string around the pulley) or...
  46. T

    Sphere Slipping Against Blocks: Solving for the Speed of the Sphere's Center

    Sphere slipping against blocks Homework Statement In the given arrangement ,a sphere of radius R is placed on the two blocks A and B where A is fixed and B is moving at a constant speed ‘v’ towards left .Find the speed of the sphere’s center when the distance between the blocks is √R and...
  47. L

    Air resistance upon a spinning block

    I came up with this problem, and solved for it, but I do question its accuracy, and id like to know how I could make it a better model. (it is not a homework problem) So, a block, of dimensions a (rests on the z axis) by b (rests on the y axis) by c (rests on the x axis), is moving with a...
  48. G

    Applied force in horizontal direction on block on a inclined plane.

    Homework Statement 10kg block on a inclined plane (32degrees) (frictionless) and an applied force 120N horizontally. What is acceleration? Homework Equations Fnet = ma The Attempt at a Solution mgsin32 = 51.9N (from mg) From applied force, in the same plane, we have xcos32=120...
  49. H

    RFID and Block Diagram Questions, help please

    Questions are shown on the pictures. For the block diagram, I know (1) error signal (5) output (7) feedback signal What are the (2), (3), (4) and (6)? Besides, how to answer the RFID questions? Ans. 1. For example, mall card? Ans. 2. Ans. 3. Ans. 4. Ans. 5. Please help!
  50. H

    The laws of motion-a block pulled by a light cord

    Homework Statement A block of mass 2.20 kg is accelerated across a rough surface by a light cord passing over a small pulley as shown in figure.The tension T in the cord is maintained at 10.0N,and the pulley is 0.100m above the top of the block.The coefficient of kinetic friction is 0.400m...
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