Exam 2: The Laws of Motion, Part 2

Suppose you take off in a car with your physics book on top. If you are accelerating forward and the book rides with you, in what direction does friction act on the book?

Suppose you are riding on a merry - go - round and you move out to the edge. Why does the rotational rate of the system decrease?

Suppose your car's speed doubles. By what factor will its kinetic energy change?

Power is

Your physics professor was laughing so hard at his own jokes that he slipped into a delirium right there in class! Before class ended he remarked that "The momentum of a larger object carries more force than that of a smaller object - that's why a Mac truck is harder to stop than a VW Bug. Please comment on the physical accuracy of his statement.

Consider a person standing on a raft, which is sitting still on the surface of calm water. -During a certain time period the person is standing still, then walks to the opposite side of the raft and then stops. Is the momentum of the raft conserved during this entire time? Please explain; ignore friction between the raft and water, air resistance, etc.

You operate a 120 W light bulb for 5 minutes. How much energy did you use?

Consider a person standing on a raft, which is sitting still on the surface of calm water. -Now suppose there is friction between the raft and water. Please discuss how your answer to part (b) will change, if at all.

Consider a person standing on a raft, which is sitting still on the surface of calm water. -During the time period described in (a) what is the net impulse delivered to the raft if friction between the raft and the water, air resistance, etc. are to be ignored?

A baseball player balances a bat on his finger; the bat is laying sideways and not standing on end. The bat will balance

You are walking with your friend along a beautiful shoreline and begin talking about physics. She says "I completely understand friction from physics class! It always acts against the motion of an object, slowing it down." Is your friend's statement accurate?

Suppose the time it takes for a wind turbine to rotate triples. By what factor will its rotational kinetic energy change?

Suppose you are changing a car tire and loosening a lug nut. You weigh 800N and stand on the end of a 2 m long wrench. How much torque do you exert on the lug nut?

When your car slides on an icy road, it is very hard to control because

You are a football player. Your coach notices that, when it has been raining and it is slippery outside, the players you tackle are rotating forward too much (their feet slip backwards). Please explain why this would show up when it is slippery outside and why contacting them a little higher when you tackle them will fix the problem.

As you come to a stop in your car, its momentum

When your car goes out of control on an icy road, it is safest to use either the clutch or gear shift to allow your car to coast and not be powered by the engine. Why is this so?

A spinning Frisbee is thrown between two persons in a park. The motion of the Frisbee is

Force and momentum are related in that:

During a July 4^th firecracker party, a pop bottle rocket laying still on the ground explodes, sending fragments everywhere. If the momentum of the pop bottle rocket (ignore friction!) initially at rest is conserved during an explosion, what can be said about the kinetic energy of various fragments after the collision?