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. T

    Bullet is fired into block at at offset, conversation of kinetic energy?

    Homework Statement Hello, first year engineering student here :)https://fbcdn-sphotos-h-a.akamaihd.net/hphotos-ak-xpf1/v/t35.0-12/10744040_871781156179440_107104578_o.jpg?oh=73c4261941e7ef6b7c682558c0925a63&oe=544F5CA4&__gda__=1414428985_0415c28b8b2e194bf0b57f065267fe49 [/B] The question is...
  2. N

    Circular motion of a steel block

    Homework Statement A .5 kg steel block rotates on a steel table, attached to a 1.20m-long hollow tube. Air is fed through the tube and is ejected from the block, giving it a thrust force of 5.21N perpendicular to the tube. Max tension the tube can withstand without breaking is 50N. Assume...
  3. A

    What is the natural force of a 25kg block that is not moving?

    What is the natural force of a 25kg block that is not moving?F=ma, g=9.81m/s^2 Attempt: (25kg)*(9.81m/s^2)= 245.25kg ?
  4. E

    What is the magnitude of acceleration for a block released up an inclined plane?

    Homework Statement 1st example: A 10 kg block is pushed up a ramp at a constant speed of 5.7 m/s. The ramp makes an angle of 30 degrees to the horizontal and the ramp is frictionless. The block is released and allowed to slide up the ramp until it stops. What is the magnitude of the...
  5. S

    Degree of freedom of a block of wood sliding on a horizontal plane

    Homework Statement Find out the degrees of freedom of a block of wood sliding on a horizontal plane. Homework Equations DoF=Nn-k N=no. of dimensions. n=no. of particles.k= no. of constraints. The Attempt at a Solution I am considering the block of wood as a rigid body made of n no. of...
  6. Emily_20

    Find the acceleration of the hanging block

    Homework Statement In terms of m1,m2, and g. find the acceleration of the hanging block in the two-block/ two-pulley setup shown in the diagram. The stands holding the string rests on the floor. All pulleys are massless, and there is no friction anywhere in the system. Homework Equations...
  7. S

    Calculating Mass of a Block in SHM with Given Parameters

    Homework Statement A block attached to a horizontal spring of force constant 75 N/m undergoes SHM with an amplitude of 0.15 m. If the speed of the mass is 1.7 m/s when the displacement is 0.12 m from the equilibrium position, what is the mass of the block? k = 75 N v = 1.7m/s @ 0.12m...
  8. J

    Get transfer function from block diagram

    Hello guys! 1 & 2: I would like to get some help to take everything in A and find transfer function at B and C. I can't find these answer... 3. I know how to go from b) to c) .. we only multiply by E(s) and B(s). But I can't find b) at first. Thanks so much! JPGraphX
  9. C

    How Fast Was the Bullet That Lodged in the Wooden Block?

    Homework Statement A 2.0-kg block of wood rests on a tabletop. A 7.0-g bullet is shot straight up through a hole in the table beneath the block. The bullet lodges in the block, and the block flies 25 cm above the tabletop. How fast was the bullet going initially? Homework Equations initial...
  10. T

    How Can I Block tankionline.com on My Mac System?

    Hi, I don't know where to ask this question so I decide to ask it here. I search all over the web and cannot find the solution. I use mac system. The website i want to block is: "tankionline.com" I used the first method stated in this webpage (http://www.wikihow.com/Block-a-Website-in-Safari)...
  11. M

    Dispersion of light through a prism and block, changing the incident angle

    There was a question in one of my study materials that asked if you increased the incident angle of white light striking the surface of a glass prism, would the colors disperse less or more. The answer was disperse more. I didn't have an answer because I saw a conflict between the two...
  12. R

    Distance traveled by a block due to unbalanced force

    Homework Statement A 60 N block in horizontal plane is pushed horizontally by force P = t^3 + 10t. The frictional resistance f = 6 - t^2. What is the distance traveled by the block after 2 seconds. Homework Equations The net force F = (t^3 + 10t) - (6 - t^2) = t^3 + t^2 + 10t - 6. The...
  13. M

    Block held at rest against a vertical wall by a horizontal force

    Homework Statement A 5.00-kg block is held at rest against a vertical wall by a horizontal force of 100 N. (a) What is the frictional force exerted by the wall on the block? (b) What is the minimum horizontal force needed to prevent the block from falling if the static coefficient of friction...
  14. P

    Pressing a Block against a Wall

    Homework Statement I have this homework question and was able to set up the free body diagrams for the two blocks but got stuck forming the equations in part a. Please help if you can and give explanations - I want to understand the concept for my test coming up. A block with mass M is pushed...
  15. A

    What Lenses Are Needed for Minimal Movement and Infinity Focus?

    Posted a while back but to no avail. I've since done some tinkering but need a little bit of help perfecting the math. I've constructed an experimental version of the above set up with success. Moving the plano-concave element away from the plano convex element brings the focal point towards...
  16. Satvik Pandey

    Block on wedge which is not fixed.Find minimum μ to keep the wedge at rest.

    Homework Statement Consider a wedge of mass m whose upper surface is a quarter circle and is smooth. The lower part is rough. A small block of same mass is kept at the topmost position and the initial position is shown in figure. The block slides down the wedge. Find the minimum value of...
  17. H

    Find Acceleration of Block M in Figure with Mass m at 0.8R

    Homework Statement The face of block M in the figure below is shaped like a semicircular bowl of radius R. A mass m is placed at the top-left corner of the bowl and then let go. Find the acceleration of block M relative to the surface it is sitting on when m is a distance of 0.8R from the...
  18. PsychonautQQ

    String with mass pulling block up frictionless ramp

    Homework Statement A block of mass M has a string of mass m attached to it. A force F is applied to the string and it pulls the block up a frictionless plane that is inclined at an angle theta. Find the force that the string exerts on the block Homework Equations F=ma The Attempt at a...
  19. F

    How does striking a block off-center affect its energy?

    Hello everyone! I was watching a Professor Lewin lecture from about 15 minutes onwards Where he talks about striking a block off-center. What is confusing me is that it seems that by striking it in a different place you are giving it more energy. This feels wrong to me because you are...
  20. blintaro

    Calculating total mechanical energy of block on spring

    Homework Statement A 5.0 kg block hangs from a spring with spring constant 2000N/m. The block is pulled down 5 cm from equilibrium position and given an initial velocity of 1.0 m/s back toward equilibrium. What are the a.) frequency b.) amplitude c.) total mechanical energy of the motion...
  21. M

    Find energy lost due to friction, and final speed of block.

    Homework Statement a 28kg block starts at rest and slides down the incline ramp which is at an angle of 20 degrees up from the horizontal. the coefficient of kinetic friction between the incline and the block is 0.22. The height of the ramp is 2.5m. How much energy was lost to friction as the...
  22. PeterDonis

    The Block Universe: Examining the Rietdijk-Putnam Argument

    [Reposted from my PF blog] The "block universe" interpretation of SR has come up repeatedly in threads here on PF. Rather than link to them, I want to summarize the key argument that is made for the "block universe" being necessary, and then summarize the arguments I made in those threads to...
  23. N

    MHB Constructing transfer block function

    Hey just needed some help working with this. I can't find any relevant textbooks and the lecture slides i have a very vague to go off from. I've attached an image, and this my attempt. I'd like to add, in my notes the lecturer used an example feedback loop and had an error signal. I am not...
  24. K

    Coefficient of friction for the block to be in equlibrium

    Homework Statement a square box held with a person's fingers pushing downward one quarter of the way along the top of the box and with their thumb pushing side wards on the bottom of the side face of the box. Friction between the person's fingers and the box is obviously very important if...
  25. Satvik Pandey

    Finding Work Done by Friction on a Sliding Block Against a Wedge

    Homework Statement Consider a fixed wedge, whose part is a quarter circle of radius as shown. A small block of mass 'm' slides down the wedge and leaves horizontally from a height 'h' as shown.The coefficient of friction between wedge and block is 'μ_{k}' . Compute the value of in centimetres...
  26. P

    Calculating Tension in a 3kg Block at 10cm from Left Side - 12N Force on Right

    Homework Statement What is the tension in a 3kg block at a point 10cm from its left side, when pulled by a string from its right side with a force of 12N The block is 30cm. Homework Equations The Attempt at a Solution So it's pretty obvious the acceleration of the block is 4 ms-2...
  27. matineesuxxx

    What Are the Accelerations of a Block and Hemisphere Sliding Together?

    Homework Statement A block of mass m slides down a hemisphere of mass M. What are the accelerations of each mass? Assume friction is negligible. (See attatchment) Homework Equations a_M = Acceleration of hemisphere N_m = Normal force of M onto m N_M = Normal force of ground onto M...
  28. M

    Block on inclined plane - pushing vs pulling

    When resolving all of the VERTICAL forces in a block that is being pushed up an incline with some incline amount theta, then when PUSHING with force P at an angle of alpha on the block, then the vertical component of force P is sin (alpha) * P in the downward direction (opposite of the Normal...
  29. O

    Write function for control system block

    Homework Statement Write function for control system block Homework Equations The Attempt at a Solution 4 and D are parallel so we add them : I am stucking in the simplication of this block Should I group these elements to a function called w[nT], so...
  30. J

    Diff Eqs for a block moving sideways down a plane

    Homework Statement I was looking at the problem discussed in the thread below. https://www.physicsforums.com/showthread.php?t=502417 A block is initially kicked in the direction perpendicular to the downslope of the plane with initial speed V. The problem asks for the speed of the block...
  31. E

    Exploring Reality: Does Block Universe Mean Time & Motion Are Illusions?

    Does block universe mean that time and motion are illusions?
  32. H

    Comparing Specific Heat Capacity of Metals A & B in Wax Block

    Homework Statement the answer is c) but i can't figure why ! is the more heat capacity substance lose and gain energy faster than the other one so it take more energy to get it's temperature raised by the same amount because it lose most of it very fast during the heating process ?
  33. T

    Equilibrium Question - at what rate does the block accelerate?

    Homework Statement A force is applied to a box 60 degrees from the horizontal. The box weights 5kg. If the force is 120N, and the surface upon which the box rests upon is frictionless, at what rate does the block accelerate? Homework Equations Fnet = ma Fg= mg The Attempt...
  34. M

    Non-european members of Warsaw Pact, Eastern Block and Comecon

    Hi, I want to discuss the non-european members of Warsaw, Pact Eastern Bloc and Comecon. For example, whati is the situation for North Korea, China and India?
  35. J

    Cylinder attached to a block on an inclined plane, rotational dynamics

    Homework Statement A cylinder of mass M and radius R, with moment of inertia: I_c = \frac{1}{2}MR^2 rolls down without slipping through an inclined plane with an angle of θ, while pulling a block of mass Mb with an attached frame (of insignificant mass) which is connected to the axis of...
  36. S

    Block sliding down an inclined plane

    Homework Statement A block takes 3 times as long to slide down an inclined plane that makes an angle of 30 degrees as it does to fall freely through the same vertical distance. Determine the coefficient of friction. Homework Equations F=μN The Attempt at a Solution I do not know...
  37. A

    Collisions - bullet shot in in block

    Three blocks (1,2,3) of mass 3.00 kg, 2.00 kg, 1.00 kg sit linearly 10.0 cm apart from each other on a frictionless surface. A 25 g bullet is shot at the first block, it travels through the first block, and embeds itself into the second block (without falling over) which then collides into...
  38. S

    Horizontal spring and wood block energy and equilibrium question

    Homework Statement A 200 g wood block is firmly attached to a horizontal spring. The block can slide along a table where the coefficient of friction is 0.40. A force of 10 N compresses the spring 18 cm. If the spring is released from this position, how far beyond its equilibrium position will...
  39. latsany

    How Governor HVG (High Value Gate) block function

    Hi, I am a student at University of Lao, Faculty of Engineering, Electrical Engineering Department I am researching about Speed Governor control system of a Hydro Power plant in my country and unfortunately, the company who owner of hydro power plant they have lost some of them papers of...
  40. W

    Has this engine cylinder/ block design be done before,would it work?

    I believe artillery guns and barrels that are highly pressurised often use shrink fitting (heating up a tube causing it to expand allowing it to be fitted over a smaller tube which it will apply an inward pressure on when it cools) to oppose the pressure from inside the barrel. Could this...
  41. M

    Minimal polynomial and diagonalization of a block matrix

    Homework Statement . Let ##X:=\{A \in \mathbb C^{n\times n} : rank(A)=1\}##. Determine a representative for each equivalence class, for the equivalence relation "similarity" in ##X##. The attempt at a solution. I am a pretty lost with this problem: I know that, thinking in terms of...
  42. BrainMan

    Non-consecutive forces with block and string

    Homework Statement a 4-kg block is attached to a string 2 m in length rotates on a horizontal surface. (a) If the co-efficient of friction between the block and the surface is .25, find the work done by the force of friction in each revolution of the block. Homework Equations Wnc=...
  43. U

    Block moving on an inclined plane

    Homework Statement A block is placed on a plane inclined at an angle θ. The coefficient of friction between the block and the plane is µ = tan θ. The block is given a kick so that it initially moves with speed V horizontally along the plane (that is, in the direction perpendicular to the...
  44. Curieuse

    Normal force on block placed on incline.2 approaches different result

    Homework Statement The problem wants me to order the choice for the directions of a force F of a constant magnitude F(a,b,c,d are unit vectors along which F has to be oriented) exerted on the block placed on an incline at 30° to the horizontal based on the normal force Fn that the incline...
  45. T

    In the block universe, what makes this particular 'now' special?

    If each person exists in an unchanging state in the block universe, and the flow of time is an illusion caused by the way memory functions[1] (or by something else, the details are not the point), then how exactly does this sensation of 'now' work? Even if 'now' is a psychological illusion...
  46. D

    MHB Interpreting a Block Diagram: How Should it be Read?

    How do we interept what is going on in the block diagram? We have u going in and being added or subtracted from noise but we arent giving the plus and minus to determine which it is. Then there is a branch off u going straight to the Kalman filter. Then y comes from the plant and is added or...
  47. B

    How Many Forces on the Bottom Block?

    Homework Statement Three blocks are stacked on top of each other. How many forces are on the bottom block? a. 0 b. 1 c. 2 d. 3 e. 4 Homework Equations The Attempt at a Solution I know this is a very simple question, I just feel like it's easy to tricked. Obviously gravity...
  48. T

    Maximum Compression of Spring in Block Collision

    Homework Statement A 1.0-kg block slides on a frictionless, horizontal air track with an initial velocity of v = 2.0 m/s. It collides with another 1.0-kg block, which is initially at rest. One end of an ideal massless spring of spring constant k = 200 N/m is attached to the second block, so...
  49. U

    Elastic collision between ball and block

    Homework Statement A block with large mass M slides with speed V0 on a frictionless table towards a wall. It collides elastically with a ball with small mass m, which is initially at rest at a distance L from the wall. The ball slides towards the wall, bounces elastically, and then proceeds to...
  50. J

    Coefficient of static friction of a sliding block

    Homework Statement block is placed on a ramp at an angle of 39.4 and height of the ramp is 1.610m and the mass of the block is 8.54kg if coefficient of kinetic friction is 0.111 and the coefficient of static friction is 0.173 what is the speed of the block at the bottom of the ramp. if it...
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