Work-energy Definition and 168 Threads

Homework Statement A locomotive exerts a 20 000 Newton force upon a train. It propels four cards, each with a 15 tonne mass. The locomotive's mass is 40 tonnes and friction is considered negligible. Initially at rest, the train accelerates over a distance of one kilometer. a) What is the...

Homework Statement A stone is thrown keeping target to a mango hanging in the branch of a mango tree. The velocity of the stone while hitting the mango is 9.8ms^-1. If the boy uses half of the energy used before the stone can reach the same height of the mango. Mass of the mango is 250gm...

Hi guys, I've got a doubt concerning to the minimum mechanical work and the work-energy theorem. Consider the following Tippens' problem (8.4): A 5-kg hammer is lifted to a height of 3 m. What is the minimum required work? The answer looks very simple and inocent, W = weight times...

The problem is that the Earth has lost all velocity and begins plummeting toward the sun. I need to find the time it takes for it to hit the sun. Note: Primes indicate "dummy variables" This solution begins with the Work K.E. Theorem...

Homework Statement Trying to derive the work-energy theorem, without manipulating differentials.Homework Equations a=\frac{dv}{dt} v=\frac{dx}{dt} W=\int F dx =ΔKE=\frac{1}{2}mvf^{2}-mvi^{2} The Attempt at a Solution F=ma \int F dx=m\inta dx =m\int\frac{dv}{dt}dx <-- I cannot continue...

I have a basic doubt on application of work energy method, 1. Can I apply work-energy method (i.e. work done equals to change in kinetic energy(KE)) for a body sliding down the inclined plane? If yes, while solving the problem i should use only change in KE or sum of change in KE &...

The apparatus above has an initial angular velocity of \omega_{1} as the rods are released. I need to find the angular velocity \omega_{2} of the apparatus at the bottom. I've tried 3 methods. First I tried a work-energy balance where I included a gravitational potential energy. KE_{1} + PE =...

Homework Statement The 8 lb uniform rod AB shown in the figure rotates in the vertical plane about a pin at C. The spring attached to the rod at D has a spring constant of 1.25 lb/in., and its unstretched length is 24in. If the rod is released from rest in the position shown, determine its...

Homework Statement A 6.0kg box moving at 3.0m/s on a horizontal, frictionless surface runs into a light spring of force constant 75 N/cm. Use the work-energy theorem to find the maximum compression in the spring. Homework Equations W = K2 - K1 W = (1/2)*m*v^2 - (1/2)*m*vo^2 W = -...

10kg block is pulled up an incline plane at 30 degree with horizontal in distance 5.0m by force 120N.coefficient of kinetic energy 0.4. help!how do you get the velocity of block? answer: v=3.48ms^-1

Homework Statement A 0.0900 kg glider is pushed up a 40.0° frictionless incline by a spring. The spring's constant is k = 640 N/m with negligible mass. The glider reaches a distance of 1.80 m along the inclined track after losing contact with the spring and then slides back down. What...

Homework Statement A 2.50-kg textbook is forced against a horizontal spring of negligible mass and force constant, k, of 250N/m, compressing the spring a distance of 0.250 m. When released, the textbook slides on a horizontal tabletop with coefficient of kinetic friction μk=0.30. Use the...

In K&K's text on mechanics, after they present the derivation of the work energy theorem: \frac{1}{2}mv^2-\frac{1}{2}mv_0^2=\int_x_0^x F(x) dx It is mentioned that since v=\frac{dx}{dt}, we could solve for \frac{dx}{dt} and integrate again to find x(t) I tried that with v_0=0 just to make...

Homework Statement The magnitude of the instantaneous acceleration experienced by an electron as it first enters the region containing the perpendicular fields is? Maximum acceleration of an alpha particle at its closest approach to a nucleus of a gold atom, expressed in s.n is...

Homework Statement Homework Equations Work done by a couple (U) = ∫M dθ Where M is the applied bending moment and θ is angle For a uniform, slender beam mass moment of inertia (I) through an axis perpendicular to the beam and passing through the centre of mass = \frac{mL^{2}}{12} If...

Homework Statement The problem is to prove the work-energy theorem: Work is change in kinetic energy.Homework Equations Line integral stuff, basic physics stuff. The Attempt at a Solution I'm given the normal definitions for acceleration, velocity and I'm given Newton's second law. I'm...

Homework Statement Block 1 is moving to the right (with velocity v1) when block two is released from rest on an incline, as shown (from height hi). They meet on the horizontal section of track. After they collide they move in opposite directions, but with the same speed. Block 2 moves...

A block (2 kg) is moving with an initial speed of 1 m/s on a horizontal rough table comes to a stop eventually. Applying work-energy theorem to the block-table system, we obtain Change in the kinetic energy of the block + Change in the kinetic energy of the table = Net work done on the...

Homework Statement At a carnival, you can try to ring a bell by striking a target with a 9.00 kg hammer. In response, a 0.400 kg metal piece is sent upward toward the bell, which is 5.00 m above. Suppose that 25.0% of the hammer's kinetic energy is used to do the work of sending the metal...

Homework Statement An extreme skier, starting from rest, coasts down a mountain that makes an angle of 25.0° with the horizontal. The coefficient of kinetic friction between her skis/snow is 0.200. She coasts for a distance of 10.4 m before coming to the edge of a cliff. Without slowing down...

Help! I am a starter physicist and I need hlep on this question stated thus: Homework Statement A sled is being pulled across a horizontal patch of snow. Friction is negligible. The pulling force points in the same direction as the sled's displacement, which is along the +x axis. As a result...

I don't understand why the force is acting through a distance of 1.2pi, even though the center of the disk clearly moves a distance of 0.6pi.

Is this answer wrong? I think they've made a mistake in the work done by the spring, which I think should be (1/2)(135)(0.5)^3?

Shouldn't there be negative work done by the string?

The work-energy theorem is stated here on Wikipedia. On the same page it says "regardless of the choice of reference frame, the work energy theorem remains valid and the work done on the object is equal to the change in kinetic energy." I am wondering if there is a relativistic version of...

Homework Statement The system shown is at rest when a constant 250N force is applied to block A. Neglecting masses of pulleys and friction, determine: a) Velocity of block B after block A moved 2 m. b) The tension in the cable http://imageshack.us/photo/my-images/259/photoivl.jpg/...

Recently I have been having issues knowing when to use the work energy principal vs. impulse momentum or using F=ma and integration. I seem to default with all problems to integrating work done over a path but then messing it up or that not being the proper approach. The issue seems to be...

Homework Statement A particle moves on a curved path from (x1, y1,z1) to (x2, y2,z2). At the start, the particle has a velocity of v = v1xi+v1yj+v1zk. This curved path can be divided into segments infinitesimally, which are, dl = dxi +dyj +dzk. It is acted on by a net force F = Fxj + Fyi +...

Homework Statement please check this link out to make it simpler to understand... http://www.scribd.com/doc/62694749/MC-Collision1D2 there is a friction block and a spring scale... it gives two measurements (the vertical force and the horizontal force) Fvertical=88.2 N and Fhorizontal=75.8 N...

Homework Statement A 34.0 kg crate is initially moving with a velocity that has magnitude 3.70 m/s in a direction 37.0 degrees west of north. How much work must be done on the crate to change its velocity to 6.08 m/s in a direction 63.0 degrees south of east? Homework Equations...

Homework Statement Suppose a hockey puck of mass m is at rest on the ice. A surly Canadian hits the puck and sends it sailing across the ice at velocity v. According to the work-energy theorem, how much work did the player's stick do on the puck?

Homework Statement A car starts at a point A at a height H above the bottom of the loop the loop. It is starting from rest and we ignore friction. A) what is minimum value of H in terms of R such that the car moves around the loop without falling off at the top point B. B) If R=20m and...

Hi, i am having a slight confusion with this theorem. I understand that if a car travels horizontally for s m at the uniform acceleration, the Net Work Done = Change in K.E. (by Work-Energy Theorem) The change in K.E. is the amount of joules required to exert the amount of Net Force on the...

Hello, I am confused about this concept. Say, a truck drives up a slope. It decelerates as it ascends. I am required to find the total work done by the engine of the truck, and I know this to be: Work done=Gain in PE + Loss in KE + Work done against friction However I'm unsure whether the...

Homework Statement A blue whale materializes 11.5 km above an airless planet with an acceleration of gravity of 6.85 m/s2. What is the speed of the whale right before impact? Use the work energy theorem. Homework Equations Work energy theorem : W = the change in k W=kf - ko w=1/2(mvf2)...

Homework Statement There is an 8 kg block on a table with a 6 kg block hanging off of a pulley on the end of a table. The rope and pulley have negligible mass, and the pulley is frictionless. The coefficient of kinetic friction between the 8.00-kg block and the tabletop is 0.250 The blocks are...

Homework Statement Figure 7-40 shows a cord attached to a cart that can slide along a frictionless horizontal rail aligned along an x axis. The left end of the cord is pulled over a pulley, of negligible mass and friction and at cord height h = 1.6 m, so the cart slides from x1 = 4.0 m to x2...

So there is this work-energy problem online that I was discussing with a friend. We both concluded with different answers and I 99.99% sure that I am correct, but there is that 0.01% chance that my understanding of physics has been completely wrong over the years. The problem is simple: A...

Homework Statement A block with mass 5 kg slides down and inclined plane with height 1.5 m and coefficient of kinetic friction .35. The final speed of the block is 4.2 m/s. Find the angle of the inclined plane.Homework Equations {W^{{\rm{net}}}} = {W^{{\rm{grav}}}} - {W^{{\rm{fric}}}} = {K_2}...

Homework Statement A skier slides down a hill, starting from rest at a height of 250m above the bottom of the hill. She skis over an intermediate hill, whose height is 100m above the bottom of the hill. If resistive forces are neglected, what is the speed of the skier a) at the top of the...

Homework Statement While running at a speed of 5.0m/s Tarzan grabs a 9.0m long vine hanging vertically from a tall tree in the jungle and swings on it. As he swings on the vine, how much work is done on him by the tension force in the vine? To what maximum vertical height can he swing if he...

Homework Statement 490 J of work is done on a pin when a 5 kg sledgehammer strikes it (bringing the sledgehammer to rest). What is the initial speed of the sledge hammer. Homework Equations (Fnet)(d)= (0.5)(m)(velocity final^2 - velocity initial^2) The Attempt at a Solution...

Homework Statement A mass m whirls on a frictionless table, held to circular motion by a string which passes though a hole in the table. The string is slowly pulled through the hole so that the radius of the circle changes from l1 to l2. Show that the work done in pulling the string equals...

Homework Statement Accident Reconstruction. A car, with a mass of 1600 kg, is involved in a collision. By using techniques from later chapters, we conclude it was moving 4 m/s at impact. There are skid marks leading into the collision, 18 meters long from two of the tires; no marks from the...

Homework Statement A box of 2Kg is projected with a speed of 6m/s up a slope at 30* to horizontal. The coeffiecient of friction is 1/3. Use the work energy principle tp calculate the distance traveled by the box before coming to rest. Homework Equations When you calculate the work done...

Homework Statement What fundamental priniple of physics does the work-energy theorum relate? Homework Equations The Attempt at a Solution is it Newton's second law?

Homework Statement In trying to lift a sandbag B attached to the rope as in the attached figure, a worker at the top of the scaffolding dumps his tools and lunch kit into the box A so that it is now 80kg. if the sandbag is 65kg, find its speed as it hits the scaffolding. Assume that the...

Homework Statement A 6kg object is lifted vertically through a distance of 5m by a light string under a tension of 80.0N. Find (a) The work done by the force of tension, (b) The work done by gravity, and (c) The final speed of the object if it starts from rest. Homework Equations W = Fd...

Homework Statement A skier comes crashing into the netting at the bottom of a ski hill. The skier has a mass of 85 kg and is moving at a speed of 65 km/h (234 m/s). (a) How much work is done by the netting while bringing the skier to rest? (b) If the "spring" constant for the netting is...

Homework Statement The masses of the javelin, discus, and shot are 0.8kg, 2kg, 7.2kg, respectively, and record throws in the track events using these objects are about 89 m, 69 m, 21 m. respectively. Neglecting air resistance, (a) calculate the minimum kinetic energies that would produce such...