Exam 2: The Laws of Motion, Part 2

Consider a person standing on a raft, which is sitting still on the surface of calm water. -Is the momentum of the raft and person taken together conserved during the time period described in (a)? Please explain. Ignore friction between the raft and water, air resistance, etc.

A child is riding a bike and skids to a stop. What happens to their kinetic energy?

What type of friction causes bearings to not waste much energy?

A baseball player throws a bat up in the air, so that it spins as it translates. The bat will rotate about its

For momentum to be conserved in a system it must

During a football game the ball is kicked and it travels across the field. If the ball is kicked away from its center of mass it will

An 800 kg car moving at 4 m/sec to the right strikes a 400 kg car moving to the left. If the cars stick together and stop moving right after the collision, what was the velocity of the 400 kg car?

If the momentum of a TNT stick (ignore friction!) is conserved during an explosion, what can be said about the momentum of various fragments of the system after it explodes?

Consider a wind turbine having moment of inertia 240,000 kg m². If a 120 kg person were holding on to the edge of the turbine 10 m from its center the torque due to the person is ________ and the angular acceleration of the turbine is ________.

Consider a sailboat with the wind gently blowing the sail on a beautiful, calm day, so the boat is propelled through the water at a constant velocity. -Is the momentum of each atom and molecule that strike the sail conserved? Please explain.

Suppose you are designing a race bicycle and it comes time to work on the wheels. You are told that the wheels need to be of a certain mass but you may design them either as wheels with spokes (like traditional bike wheels) or you may make them as having solid rims all the way through. Which design would you pick given that the racing aspect of the machine is the most important? Please explain.

Suppose you are riding a bicycle. If you want to waste as little energy as possible while the bike is in motion, what type of friction should exist between the bike and the road?

A person is running a potter's wheel, where they use their feet to run pedals that turn a large disc they can put clay on. Suppose the disc is turning and some clay is dropped straight down on the rotating wheel, which slows down a little. Why did the wheel slow down when the clay was dropped on it, and where on the wheel should the clay be placed so that it is easiest for the potter to speed the wheel back up again? Please explain.

Sliding friction is not desirable in wheel bearings because

An object pivoting about its center of mass is

Suppose your car is traveling at a certain speed on a very slick road. All of a sudden you step on the accelerator and the back wheels begin to spin but the car remains at the same speed. The kinetic energy of the car

Drive shafts in cars are long metal tubes that transfer power to the axles from the engines through spinning very rapidly. Why can it severely damage your car if the drive shaft is not balanced?

Consider a sailboat with the wind gently blowing the sail on a beautiful, calm day, so the boat is propelled through the water at a constant velocity. -Is the momentum of the boat conserved? Please explain.

What does friction not depend upon?

Suppose the time it takes for the moon to rotate doubles. By what factor will its rotational kinetic energy change?