**Your Answer to Q410.**
Sorry, your answer is **not** correct. Work requires a force acting through
a distance.

Help: *Fundamentals of
Sound*, Sec. 10-A.

Or would you like a **HINT**?

You should try to work out the answer on your own, but if you insist on reading it the correct answer is here

Return to Question 410.

**Hint
for Question 410:** Work requires a force acting through a distance;
a distance counts *only* if it is in the direction of the force. Assume
that the skater is just gliding without pushing off. Does that make a difference?

Return to Question 410.

**Your
Answer to Q410. **Congratulations, your answer is **correct**.

If you would like, you can compare your answer to the "official" correct answer

Return to Question 410.

**Correct
Answer to Question 410:** d) is the correct answer. Gravity is doing
work on the book since it is falling through a distance while acted by a force
equal to the weight of the book. The child is pulling the truck, which causes
a force along the distance pulled. If the skater is not pushing off, but is
just coasting, he is doing no work. (if you assumed he *is* pushing off
and gaining kinetic energy, then he would also be doing work, however the problem
says he is just gliding.) The only force he is exerting is upward to hold his
partner in the air. That force is vertical, but the distance moved in the problem
is the horizontal displacement of the pair. So the force does not act in the
direction of the distance moved and no work is done by the force. Note that
the pair has kinetic energy, but that the kinetic energy and the potential energy
of the partner are not changing, because he is doing no work on her. When he
first lifted her over his head he certainly did work and she gained the potential
energy that she now has.

Return to Question 410.

**Your Answer to Q420.** Sorry, your answer is
**not** correct. Work is done when a force acts through a distance.

Help: *Fundamentals of
Sound*, Sec. 10-A.

Or would you like a **HINT**?

You should try to work out the answer on your own, but if you insist on reading it the correct answer is here

Return to Question 420.

**Hint
for Question 420:** The distance that counts is that which is along
the applied force. What workers are pushing through a distance that is along
their force?

Return to Question 420.

**Your
Answer to Q420. **Congratulations, your answer is **correct**.

If you would like, you can compare your answer to the "official" correct answer

Return to Question 420.

**Correct
Answer to Question 420:** b) is correct because the workers 2 and 4
are pushing perpendicular to the displacement of the piano and are doing *no*
work. Workers 1 and 3 are pushing along the direction of the displacement, doing
work, and increasing the piano's kinetic or potential energy.

Return to Question 420.

**Your
Answer to Q425.** Sorry, your answer is **not** correct. Will the
book continue to gain velocity as it falls further?

Help: *Fundamentals of
Sound*, Sec. 10-A.

Or would you like a **HINT**?

You should try to work out the answer on your own, but if you insist on reading it the correct answer is here.

Return to Question 425.

**Hint
for Question 425:** Note that the book is still a certain distance from
the floor. Gravity is still pulling on it.

Return to Question 425.

**Your
Answer to Q425. **Congratulations, your answer is **correct**.

If you would like, you can compare your answer to the "official" correct answer HERE.

Return to Question 425.

**Correct
Answer to Question 425:** The book has lost some potential energy by
falling half way to the floor, but it is still has some distance to fall so
that it still has some potential energy. The answer is c). As it falls farther,
gravity continues to do work on it so it gains more kinetic energy and loses
even more potetial energy. It will not have lost all of its potential energy
until just before it hits the floor where it will have converted all of its
potential energy to kinetic energy.

Return to Question 425.

**Your
Answer to Q430.** Sorry, your answer is **not** correct. A diagram
of the trajectory of the diver might help. Actually, there is a way you might
have drawn your diagram that might make your choice of answer correct after
all!

Help: *Fundamentals of
Sound*, Sec. 10-A.

Or would you like a **HINT**?

You should try to work out the answer on your own, but if you insist on reading it the correct answer is HERE.

Return to Question 430.

**Hint
for Question 430:** If she is moving forward at the highest point she
still does have kinetic energy. The correct answer depends on the trajectory
you assumed for the diver.

Return to Question 430.

**Your
Answer to Q430. **Congratulations, your answer is **correct**. (That is,
it is correct *if* you have chosen the same trajectory as we show in the
correct answer!)

If you would like, you can compare your answer to the "official" correct answer HERE.

Return to Question 430.

**Correct
Answer to Question 430:** See the two possible trajectories in the figure.
In the A trajectory the diver goes almost straight up before she starts down.
At the top she has no velocity—she has stopped momentarily. She thus has
*no* kinetic energy and all her energy is **potential**. She is accelerating
and gravity will soon convert her potential energy into kinetic energy. In this
case the answer is b). In trajectory B, she is still going forward at the highest
point of her dive because she initially jumped forward as well as up. So at
that point she has both kinetic energy and potential energy. In this case the
answer would be c). Sorry if we said you were wrong if you used trajectory B!

Return to Question 430.

**Your
Answer to Q435.** Sorry, your answer is **not** correct. What
does the ball do when it reaches the bottom?

Help: *Fundamentals of
Sound*, Sec. 10-A.

Or would you like a **HINT**?

You should try to work out the answer on your own, but if you insist on reading it the correct answer is HERE.

Return to Question 435.

**Hint
for Question 435:** The ball continues to roll when it reaches the bottom.

Return to Question 435.

**Your
Answer to 435. **Congratulations, your answer is **correct**.

If you would like, you can compare your answer to the "official" correct answer HERE.

Return to Question 435.

**Correct
Answer to Question 435:** The ball continues to roll when it reaches
the bottom. It has converted all of its potential energy that it had at the
top of the ramp into kinetic energy so it continues moving on with that energy.
The answer is a).

Return to Question 435.

**Your
Answer to Q440.** Sorry, your answer is **not** correct. How does
the string store potential energy?

Help: *Fundamentals of
Sound*, Sec. 10-C.

Or would you like a **HINT**?

You should try to work out the answer on your own, but if you insist on reading it the correct answer is HERE.

Return to Question 440.

**Hint
for Question 440:** The string stores potential energy elastically by
being stretched. It will release this by bouncing back to its unstretched state.

Return to Question 440.

**Your
Answer to Q440. **Congratulations, your answer is **correct**.

If you would like, you can compare your answer to the "official" correct answer HERE.

Return to Question 440.

**Correct
Answer to Question 440:** In a) and c) the string is stretched so that
it has some potential energy—much like a stretched spring. At a) the string
is momentarily at rest (somewhat like the diver at the top of her dive in trajectory
A of Question 430). In c) the string is again stretched somewhat, but
it is also moving, and so has both potential and kinetic energies. At the extreme
point of the string's motion downward (not shown) it would again have no KE
and its energy would be all PE. At b) the string is not stretched at all, but
is is moving as fast as it ever does. So at b) it has all kinetic energy and
no potential energy. (Note we have neglected gravity in our discussion because
it plays such small role in changing the potential or kinetic energy of the
string. You could think of the string as vibrating horizontally so that gravity
plays on role at all. )

Return to Question 440.

ab_webmaster@abacon.com

©2002 William J. Mullin

Legal Notice