Friction Problems

1. A 20.0 kg mass is pulled by along a surface by a horizontal force of 100 N. Friction is 20.0 N.

Draw a Free Body Diagram.

What is the acceleration of the mass?

2. A jet engine generates 160 kN of force as it propels a 20,000kg plane down a runway. If 40 kN of friction opposes the plane, how much time it will take the plane to reach a speed of 33m/s from rest?

3. What does equilibrium mean?

4. There are two things that can be happening for an object to be in equilibrium. Describe each:

a)

b)

5. A 49-N block is pulled by a horizontal force of 50.0 N along a rough horizontal surface at a constant acceleration of 6 m/s/s.

What is the coefficient of friction?

6. A 15.0 kg block is pulled by a horizontal force of 30.0 N along a rough horizontal surface at constant velocity. What is the coefficient of friction?

7. If the coefficient of kinetic friction between a 35 kg crate and the floor is .30, what horizontal force is required to move the crate at a steady speed across the floor? What horizontal force is required if µk is zero?

8. A car is traveling at 60.6 mph on a horizontal highway. The acceleration of gravity is 9.8 m/s2. If the coefficient of friction between road and tires on a rainy day is 0.056, what is the minimum distance in which the car will stop? Answer in units of m.

9. A 200 kg golf cart is traveling at 15 m/sec on a surface with a coefficient of kinetic friction equal to 0.5. The driver slams on the brakes to avoid a crossing squirrel and locks the tires.
a) draw a free body diagram

b) what is the kinetic friction force used to stop the cart?
c) how much time does it take the cart to stop?

d) what is the acceleration of the cart?

e) what distance will it take to stop?

10. A 4.0 kg toboggan rests on a frictionless icy surface and a 2.0 kg box rests on top of the toboggan. The coefficient of static friction between the box and toboggan is 0.60, whereas kinetic friction coefficient is .51.. The box is pulled by a 30 N force along the horizontal parallel to the icy floor. What are the magnitudes and directions of the resulting accelerations of the block and toboggan? Don’t solve this problem. Do draw a picture and label the forces involved.