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 Free problems: all problems
 Kinematics Dynamics Conservation laws Thermodynamics Waves Electricity Magnetism Optics Fluids and elasticity Ideal gas AC current

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# Physics problems:dynamics

Static and kinetic friction

Problem 11.

A box is sliding up an incline that makes an angle of 20 degrees with respect to the horizontal. The coefficient of kinetic friction between the box and the surface of the incline is 0.2. The initial speed of the box at the bottom of the incline is 2 m/s. How far does the box travel along the incline before coming to rest?

Solution

Problem 12.

A block weighing 80 N rests on a plane inclined at 30 degrees to the horizontal. The coefficients of static and kinetic friction are 0.2 and 0.1 respectively. What is the minimum magnitude of the force F, parallel to the plane, that will prevent the block from slipping?

Solution

Problem 15.

A car (m=2000 kg) is parked on a road that rises 20 degrees above the horizontal. What are the magnitudes of (1) the normal force and (2) the static frictional force that the ground exerts on the tires?

Solution

Problem 19.

A dancer is standing on one leg on a drawbridge that is about to open. Before the drawbridge starts to open, it is perfectly level with the ground. The dancer is standing still on one leg. What is the x component (horizontal component) of the friction force?

Solution

Problem 20.

A block of mass 5 kg lies on a horizontal table. The block is at rest. The only forces acting on the block are the force due to gravity and the normal force from the table. What is the magnitude of the friction force?

Solution

Problem 21.

Starting from rest, a skier slides 200 m down a 35 degrees slope. How much longer does the run take if the coefficient of kinetic friction is 0.3 instead of 0?

Solution

Problem 28.

Is it easier to move a heavy box that is sitting on the ground by (a) pulling the box from a rope that makes an angle with the surface or (b) by pushing the box with a force that makes the same angle (but pointing downwards) with the surface?

Solution

Problem 31.

A circus clown weighs 900 N. The coefficient of static friction between the clown's feet and the ground is 0.4. He pulls vertically downward on a rope that passes around three pulleys and is tied around his feet. What is the minimum pulling force that the clown must exert to yank his feet out from under himself?

Solution

Problem 46.

A hotel guests starts to pull an armchair across a horizontal floor by exerting a force of 91 N 15 degrees above the horizontal.  The normal force exerted by the floor on the chair is 221 N up.  The acceleration of the chair is 0.076 .  Determine the mass of the chair.

Solution

Problem 48.

A block of mass m is kept on a horizontal ruler. The friction coefficient between the ruler and the block is . The ruler is fixed at one end and the block is at a distance L from fixed end in the horizontal plane through the fixed end. What can the maximum angular speed be for which the block does not slip?

Solution

Problem 52.

A 35 kg crate undergoes a horizontal acceleration of  on a level surface when pulled by a 65.0 N force. What is the coefficient of kinetic friction between the crate and the surface?

Solution

Problem 53.

A block of mass 13.6 kg is sliding at an initial velocity of 4.65 m/s along horizontal surface to the right. The surface has a coefficient of kinetic friction of 0.254. How far will it slide before coming to rest?

Solution

Problem 54.

A 2.65 kg crate is held in static equilibrium on an incline of angle 35.0 degrees by a force F applied perpendicular to the incline. The coefficient of static friction between the crate and the incline is 0.255. Determine the minimum magnitude of F that keeps the crate in static equilibrium.

Solution

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