+ANSWERS TO:
_____________________________Physics
109 Test 1
(your
name) Circle the correct
letter or write in the correct answer
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1. You have built a
bungee-jumping amusement that permits your customers to enjoy a seven second
free-fall (you may assume that g = 10m/s). After that fall,
(Ans.
= d.) Since there is no initial x or
initial v, v = at and x = ½ at2
2. The reason that a pendulum
clock keeps good time is:
(Ans.
= b.) See the text page 234.
3. The radiation from the
surface of our sun, which is at about 6000K, is:
Ans.
= b. (see Fig
6.2.4, page 200))
4. A man and a small child
are sitting at the center of a perfectly slippery ice skating rink but do not
have skates. They are not moving and the man realizes that the only way for
them to get off the rink is for the pair to push one another off the ice.
Before the man can act, the child pushes hard on the man and the man begins to
slide across the ice toward the edge. The man had no time to push the boy and,
therefore:
Ans.
= d; they will have equal and opposite momentum
5. When you drop a rubber
ball on the floor and its bounces, the direction of its velocity reverses
because:
Ans.
= d.
6. Moment of
inertia is the measure of an object’s rotational inertia. If you wanted to
figure out which of two round, symmetric objects has the largest moment of
inertia, you should
(a)
spin each object in your hand and then drop it to the
floor. The one that falls fastest while spinning has the larger moment of
inertia.
(b) lift
each object and see which one takes the most force to lift upward at constant
velocity.
(c) twist
each object back and forth about its center and see which one responds least
rapidly.
(d)
spin each object in your hand and then drop it to the
floor. The one that falls slowest while spinning has the larger moment of
inertia.
Ans.= c; Large moment of inertia => large resistance to
angular acceleration.
7. A large truck breaks down
out on the road and receives a push back into town by a small compact car.
While the car pushing the truck is speeding up to get up to cruising speed:
Ans.
= b;
8. Dew that forms on the
grass and ground:
Ans. = d. Heat is required to evaporate water and thus
we expect heat to be given up when water vapor condenses.
9 You are pushing a
refrigerator across a wood floor in a straight line and at a steady speed.
Therefore,
Ans.
= c; No net horiz. force so you and friction are
equal and opposite.
10. When we increased the
temperature of a hot filament in an incandescent light in class we noted that
the thermal radiation:
Ans.
= d. Hoitter
surfaces both emit more radiant energy (per square meter) but also shift their
peak radiation to higher frequencise (and thus to
shorter wavelengths)
11. Energy from the sun
reaches the earth
Ans.
= a. Radiation only
12. Suppose the river next to
a power plant rises in temperature by 20 degrees C in summer. Would you then
expect the efficiency of the power plant which uses that river for cooling
water to:
Ans.
= b. When the “low side temperature” of
a heat engine is raised (or the “hot” side lowered) the ideal efficiency is
reduced.
13. A diver whose mass is 40kg
steps off a diving board that is 10m above the water. The diver hits the water
with kinetic energy of (approximately):
Kat
bottom = Pat top = mgh => Answer
c.
14. A 1000 kg car moving at
50m/s south on slick ice hits a 5000 kg truck and the pair are
stuck together and at rest immediately after the collision. The truck velocity
before the collision was:
Ans. = d. Total momentum of this system before collision
must have been zero.
15.
A two-kilogram mass is held by a vertical spring. The spring is stretched by
that mass 16 centimeters from its equilibrium length. If you now add 1.5
kilograms to the existing mass, how far will the spring be stretched from its
equilibrium length?
a. 20 cm. b.
24 cm. c. 26 cm. d. 28 cm.
Ans.
= d. F = -kx
; F has been increased from 20N to 35N
16.
If you drop a golf ball and a bowling ball simultaneously from the roof of your
house, they will both hit the ground simultaneously. The two balls travel
downward side by side because gravity gives them identical:
a. Downward momenta.
b. Downward acceleration
c. Masses
d. Downward force
Ans.
= b.
17.
If you try to cook vegetables with warm air at 150 degrees C., it takes a very
long time. But when you cook those same vegetables with 100 degrees C. steam,
they cook very rapidly. This is because the steam:
a. condenses on the colder vegetables, releasing a
large amount of heat.
b. causes moisture inside the vegetables to boil and
transfer heat to the vegetables.
c. condenses on the colder vegetables and absorbs a
large amount of heat from the vegetables.
d. causes moisture inside the vegetables to boil and
absorb heat from the vegetables.
Ans. = a.
Condensing steam releases much more heat than an equal mass of air at
the same temperature.
18. You were heading forward in your car before coming
to a complete stop at a red light. The careless driver of the car behind you
fails to stop and his car crashes into your car from behind. You suddenly find
your head shifted deep into the elastic cushion of your seat's headrest. During
the period when your head is deep in the cushion, the net force on your head is
a) backward
and its acceleration is backward.
b) forward
and its acceleration is forward.
(c) backward
and its acceleration is forward.
(d) zero
and it is not accelerating.
Ans. = b.
19. A woman
leaps off the high diving board during a swimming competition and does a series
of flips and spins in the air. As she plunges toward the water, her
(a) angular
velocity is constant.
(b) angular
momentum is constant.
(c) momentum
is constant.
(d) velocity
is constant.
Ans. = b. With
no external torques, her ang.
mom. is constrant. She does experience an external force
(gravity)
20. Suppose you
have two identical-looking sticks, each with exactly the same total mass. In
one stick, most of the mass is located at its ends. In the other stick, most of
the mass is located at the middle. If you grip both sticks at the middle and
exert equal torques on them with your wrists,
(A) the sticks will undergo equal
accelerations because they have equal masses.
(B) the stick with its mass near its
ends will undergo more angular acceleration.
(C) the stick with its mass near its
middle will undergo more angular acceleration.
(D) the sticks will undergo equal
accelerations because they have equal moments of inertia.
Ans.
= c. More mass at the ends means greater
moment of inertia meaning less angular accel.for the
same applied torque.
21. You shoot an arrow at a target and it heads
for the bullseye. After the arrow has left the bow, which of the following most
accurately describes the force pushing it forward during its flight?
(A)
The arrow experiences no forward force.
(B) The forward force is constant all the way to the bullseye.
(C) The forward force increases to the midway point and then decreases to zero
just as the arrow hits the bullseye.
(D) The forward force decreases steadily, reaching zero just as the arrow hits
the bullseye.
Ans. = a. (But b is not wrong and was accepted)
22. A helicopter is hovering motionless above a
disabled boat, while rescue workers use a rope to lift an injured sailor. While
that sailor is being lifted upward, the net force on the motionless helicopter
is
(A)
downward and equal to the sailor's weight.
(B) zero.
(C) upward and equal to the sailor's weight.
(D) downward and equal to the sailor's weight plus the helicopter's weight.
Ans. = b. Motionless => no net
force.
23. You're heading northward in your car. The
light turns red in front of you, so you step on the brake. As you do,
(A) your car's velocity is southward.
(B) your car accelerates northward.
(C) your car accelerates southward.
(D) the net force on your car is zero.
Ans.
= C. The brakes are exerting a southward
accel in order to slow the car.
24. When an ice skater begins to spin on the
point of one skate, her arms are outstretched. She then pulls in her arms and
spins much more rapidly because
(A) her angular momentum can't change but her moment
of inertia decreases.
(B) her mass decreases so the force of her momentum
causes her to accelerate.
(C) her angular velocity can't change so her angular
acceleration must increase.
(D) her angular acceleration can't change so her
angular velocity must increase.
Ans.
= A.
25. You are walking your dog on a leash. The dog
sees a rabbit and begins to run after it. The two of you run across the park,
with the dog in the lead and you following. The leash is tight. As the two of
you run,
(A) you are transferring equal amounts of energy to
one another.
(B) there is no transfer of energy between you and the
dog.
(C) the dog transfers energy to you.
(D) you transfer energy to the dog.
Ans. = c. The dog is pulling you in the direction you
are moving and thus the leash must be doing work on you.
26. During the power
stroke in one cylinder of a car's engine, the burned fuel and air gases push
the piston out of the cylinder. In accordance with
(A) the burned gases do work on the piston and they experience a drop in temperature.
(B) the burned gases do work on the piston and they experience a rise in temperature.
(C) the piston does work on the burned gases and they experience a drop in temperature.
(D) the piston does work on the burned gases and they experience a rise in temperature.
Ans. = a. Gasses push on the piston; expanding gas will drop in temperature.
27. A friend suggests that you invest in a new invention that apparently absorbs heat from the room and converts it into electricity. It supposedly sits in the middle of the room, gradually cooling the room air while providing a steady and endless supply of electric power. You wisely choose not to invest because in order to work as described, this device would have to do something impossible-it would have to
(A) violate the conservation of energy.
(B) lower the total entropy of its environment.
(C) turn stored energy into power.
(D) turn work into heat, or more precisely, into thermal energy.
Ans. = B
28. You’re operating a propane gas grill from a fuel tank that’s located below the grill. This tank is half filled with liquid propane. As the grill consumes gaseous propane, the tank’s temperature drops below room temperature. This refrigerating effect occurs because
(A) heat naturally flows from a cooler object to a hotter object.
(B) heat is needed to initiate and sustain combustion in the grill.
(C) thermal energy is being used to convert liquid propane into gaseous propane in the tank.
(D) heat naturally rises from the tank to the grill above it.
Ans. = C. Whenever we turn a liquid into a gas we must supply heat.
29. A heat engine produces useful work as it transfers heat from a hot region to a cold region. If the cold region's temperature increases and the hot region's temperature stays constant, the heat engine will
(A) need to transfer more heat to produce the same amount of useful work as before.
(B) become more efficient than before at converting heat into useful work.
(C) have the same efficiency as before at converting heat into useful work.
(D) be able to produce more useful work while transferring the same amount of heat as before.
Ans. = a. Efficiency is lowered when either high temp drops or lower temp increases.
30. The temperature of a glass of ice water (a mixture of ice and water)
(A) is proportional to the ratio of water to ice.
(B) depends on the total volume of ice and water in the glass.
(C) is 0 °C.
(D) is proportional to the ratio of ice to water.
Ans. = c.
31. A heat engine provides usable work by permitting:
A. Heat to flow from a colder object to a hotter object.
B. Work to be completely transformed into heat.
C. Heat to be completely transformed into work.
D. Heat to flow
from a hotter object to a colder object.
Ans. = D.
33. The heat capacity of liquid water is 1 calorie per gram per degree Celsius (or 1 Calorie = kilocalorie per kg. per degree Celsius). This means that:
A. If I have 10 g of water, I can raise its temperature 1 degree Celsius by adding one calorie of heat.
B. If I have 10 g of water, I can raise its temperature 10 degrees Celsius by adding 10 calories of heat.
C. If I have 1000 kg of water, I can raise its temperature by 10 degree Celsius by adding 1 Calorie of heat.
D. None of the above.
Ans. = D.
SHORT, DIRECT ANSWERS PLEASE
34. A compact tumbling space
satellite suddenly extends a very long boom-antenna while rotating in space.
Its speed of rotation (in revolutions per second) will: (state why you give the
answer below)
Ans = b. Because: We have increased the moment of inertia
and thus, in the absence of an external torque, the angular momentum remains
constant and the angular velocity slows. ________________________________
35. What was the particular
physical observation made by Benjamin Thompson (Count Rumford) in his drilling
of canon that caused him to correctly deduce the origins of thermal energy?
Ans. = Drilling a canon with
a very dull drill appeared to release the same amount of heat as when using a
very sharp drill. Thus, heating was not
the result of the “release of caloric”.