1) The coefficient of kinetic friction between a 20 kg box and the floor is 0.40. A horizontal rope pulls the box across the floor at a constant speed.
a) What is the normal force acting on the box?

b) What is the friction force acting on the box?

c) How much work does the rope do on the box in pulling it 8.0 m across the floor?

d) Suppose the rope acts at an angle of 37o upward from the horizontal instead of horizontal. What is the normal force in this case?

e) What work is done by the rope if the angle is 37o and the box moves 8.0m?

2) A car is held on a 25 degree incline by a cable attached to a tow truck (as shown). The car has a mass of 2000kg, don't worry about friction.

a) What is the normal force acting on the car?

b) What is the tension in the cable?

c) What would be the acceleration of the car if the cable breaks, at the instant it breaks?

3) The concrete barrier between the north bound and south bound lanes of traffic on I-65 at the bridge are about 1.5 m high. How fast would a 2000kg truck have to be going to have enough energy to flip over the barrier if you assume all the kinetic energy is converted into potential?

4) In the following picture of a roller coaster h1= 10m, h2 = 4m, h3 = 7m and h4 = 8m.
a) If the car starts at rest at A and assuming no friction, what is the speed at D? (Hint: Do you really care what happens at B and C?)

b) Suppose the car starts at A with a velocity of 2m/s. What is the speed at D, again assuming no friction?

c) Suppose there is friction. How much work would be done by friction if the car starts with zero speed and reaches C with a velocity of 0?

5) A 3kg box slides across a frozen pond with zero friction. Initially it is moving at 4m/s. Rain begins to fall so that after a while the box has collected 0.2kg of rain water.
a) Is the rain falling into the box an elastic or inelastic collision and how do you know?

b) What is the final velocity of the box after collecting 2kg?

6) Some rotation questions; 2 points each.

a) When a high diver wants to turn a flip in midair, she draws her legs up into a tuck. Why does this make her rotate faster and which principle of physics is involved here?

b) Explain the two conditions of equilibrium.

c) Communication satellites have antennae that must always point in the same direction. This can be accomplished by causing the satellite to spin. Why does this help and what principle in physics is used here?

d) Give the conditions in which an automobile driver can have a centripetal acceleration but have no tangential acceleration.

e) A coin is thrown off a turntable when the table rotates too rapidly. In the diagram, which is the correct path of the coin when viewed from above and why?

f) Explain how a child on a swing can cause the swing to rise higher and higher with out touching the ground by pumping his feet back and forth.

g) Which would be easier to stop, a rotating bicycle tire filled with air or one filled with water? Explain.

h) In the demonstration last Tuesday, why does the solid wheel go down the ramp faster than the hollow wheel (they have the same mass and radius)?

I) Why does a spinning top not turn over?

j) Does the force of gravity which keeps a satellite in orbit exert any torque on the satellite? Why or why not?

Bonus:
In the lab on conservation of energy a good thing to do with the velocities in part one was find a confidence limit. But you did not want to do that with the velocities in part 2. Why?

What are Kepler's laws?

What is the universal law of gravitation?