Object 1 pushes on object 2 as the objects move

together, like a bulldozer pushing a stone. Assume

object 1 does 15.0 J of work on object 2. Does object 2

do work on object 1? Explain your answer. If possible,

determine how much work and explain your reasoning.

A student has the idea that the total work done on an

object is equal to its final kinetic energy. Is this idea true

always, sometimes, or never? If it is sometimes true,

under what circumstances? If it is always or never

true, explain why.

(a) For what values of the angle $$\theta$$   between two vectors

is their scalar product positive? (b) For what values of $$\theta$$  

is their scalar product negative?

Can kinetic energy be negative? Explain.

Discuss the work done by a pitcher throwing a baseball.

What is the approximate distance through which the

force acts as the ball is thrown?

Discuss whether any work is being done by each of the

following agents and, if so, whether the work is positive

or negative. (a) a chicken scratching the ground

(b) a person studying (c) a crane lifting a bucket of

concrete (d) the gravitational force on the bucket in

part (c) (e) the leg muscles of a person in the act of

sitting down

If only one external force acts on a particle, does it necessarily

change the particle’s (a) kinetic energy? (b) Its

velocity?

Preparing to clean them, you pop all the removable

keys off a computer keyboard. Each key has the shape

of a tiny box with one side open. By accident, you spill

the keys onto the floor. Explain why many more keys

land letter-side down than land open-side down.

You are reshelving books in a library. You lift a book

from the floor to the top shelf. The kinetic energy of

the book on the floor was zero and the kinetic energy

of the book on the top shelf is zero, so no change

occurs in the kinetic energy, yet you did some work in

lifting the book. Is the work–kinetic energy theorem

violated? Explain.

A certain uniform spring has spring constant k. Now

the spring is cut in half. What is the relationship

between k and the spring constant k' of each resulting

smaller spring? Explain your reasoning.

Does the kinetic energy of an object depend on the

frame of reference in which its motion is measured?

Provide an example to prove this point.

Cite two examples in which a force is exerted on an

object without doing any work on the object.