A 78-kg skateboarder grinds down a hubba ledge that is D m long and inclined at M° below the horizontal. Kinetic friction dissipates half of her initial potential energy to thermal and sound energies. What is the coefficient of kinetic friction between her skateboard and the ledge surface?

A 2.46 kg block moves along a frictionless surface with a speed of 7.83 m/s when it encounters a rough shallow hill, whose sides have a length of l=5.21 m. The hill is low enough so that the block can make it over the hill. Because the surface of the hill is rough (shown in orange in the figure), the block experiences a frictional force of 2.23 N while on the hill. a) What is the speed of the block after it traverses the hill?

A block of mass m is on an inclined ramp. The ramp makes anangle θ with respect to the horizontal, as shown. The ramp hasfriction, with coefficient of kinetic friction μk and static friction μs.This experiment takes place on earth.The block has an initial speed of v up the ramp. It travels adistance d along the ramp before it stops.Answer using variables, please d) Calculate the work done by the Friction force as the block travels the distance d.Is it positive, negative, or zero?e) If the block comes to rest, how far has it travelled?Use the work-energy principle and your results of parts b), c), and d).f) Briefly (one sentence) explain why this problem could not be solved using conservation ofenergy.

A 7.80 g bullet is moving at 460 m/s just before it penetrates a tree trunk to a depth of 4.9 cm (ay What the magnitude of the average frletional force (In N) that is exerted on the bullet whille moving the tree trunk? Uso work considerations to o your answer. (b) Asturing the frictional force is constant, how much time elapses between the moment the bullet enters the tree trunk and the moment it moving?

A 7.80-g bullet moving at 640 m/s penetrates a tree trunk to a depth of 6.10 cm. (a) Use work and energy considerations to find the average frictional force that stops the bullet. (b) Assuming the frictional force is constant, determine how much time elapses between the moment the bullet enters the tree and the moment it stops moving.

A 35 kg sled slides along a horizontal surface on which the coefficient of kinetic friction is 0.25. Its velocity at point A is 10.0 m/s, and its velocity at point B is 2.0 m/s. You must use Work/Energy methods (not Kinematics). (a) What is the frictional force acting on the sled? (b) How much work is done on the sled by friction over the displacement ∆x = xB − xA? (c) What is the distance the sled travels between A and B?

A 59.0-kg box is being pushed a distance of 6.70 m across the floor by a force P whose magnitude is 186 N. The force P is parallel to the displacement of the box. The coefficient of kinetic friction is 0.239. Determine the work done on the box by each of the four forces that act on the box. Be sure to include the proper plus or minus sign for the work done by each force. (a) Wp = i (b) W = (c) Wmg= i (d) WN= i

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A 7.80-g bullet moving at 600 m/s penetrates a tree trunk to a depth of 4.50 cm. (a) Use work and energy considerations to find the average frictional force that stops the bullet. ____________________ N(b) Assuming the frictional force is constant, determine how much time elapses between the moment the bullet enters the tree and the moment it stops moving._____________________ s