Download GSCI 101A - Section 006

GSCI 101A - Practice Exam
Universal Gravitational Constant = G = 6.67 x 10-11 N·m2/kg2
gravitational acceleration of free fall near Earth's surface = g = 9.80 m/s2
Stefan-Boltzmann constant =  = 5.67 x 10-8 J/(m2sK4)
Boltzmann constant = kB = 1.38 x 10-23 J/K
Universal Electrostatic Constant = 8.99 x 109 Nm2/C2
1. Your weight is
a) actually your mass.
b) the gravitational attraction between you and the Earth.
c) a result of you being in mechanical equilibrium.
d) both b) and c).
b) the gravitational attraction between you and the Earth.
2. The Earth has a mass of 5.98 x 1024 kg; the Moon has a mass of 7.35 x 1022 kg and
orbits the Earth at a distance of 3.84 x 108 m. What is the gravitational force of attraction
between the Earth and the Moon?
a) 2.98 x 1030 N
b) 1.99 x 1020 N
c) 7.63 x 1028 N
d) 7.20 x 1023 N
b) Fgravity = GmM/r2 = 6.67 x 10-115.98 x 10247.35 x 1022/(3.84 x 108)2 = 1.99 x 1020 N.
3. An object is thrown upwards near the surface of the Earth with a speed of 5.21 m/s.
What is the velocity of the object after 3 seconds?
a) 5.21 m/s, up
b) 34.6 m/s, down
c) 29.4 m/s, down
d) 24.2 m/s, down
d) v = v0 + at = 5.21 + (-9.80) 3.00 = -24.2 m/s, i.e., 24.2 m/s downwards.
4. What must be the net force applied to a mass of 18 kg being accelerated at a rate of
0.35 m/s2?
a. 6.3 N.
b. 51 N.
c. 0.019 N.
d. 0 N.
a. F = ma.
5. Gary Jeter throws a baseball from an initial speed of zero to a final speed of 30 m/s in
0.20 seconds. What is the average acceleration of the baseball while he's throwing it?
a) 6.0 m/s2
b) 30 m/s2
c) 150 m/s2
d) 750 m/s2
c) a = v/t = (30 - 0)/0.20 = 30/0.2 = 150 m/s2.
6. Kepler’s third law of planetary motion states: “The square of any planet’s period of
revolution (T) is directly proportional to the cube of the planet’s average distance (R)
from the Sun.” A mathematical statement of this law (where k is a constant) is
a. T = kR 2 /3.
b. T = kR 3 /2.
c. T 2 = k/R 3 .
d. T 3 /2 = k/R.
b.
7. Which of the following statements (A-D) is not true for both a genuine science like
astronomy and a pseudoscience like astrology?
a. They both make predictions.
b. They may both use modern computer technology to calculate positions and
movements of the heavenly bodies.
c. They both include the belief that heavenly bodies affect certain phenomena on
earth.
d. All the statements above are true.
d.
8. A force of 15 N pushes a 3.0-kg object 4.3 m across a floor. The work done by this
force is
a) 22 J
b) 190 J
c) 65 J
d) depends upon the frictional force acting on the object.
c) W = Fx = 154.3 = 65 J.
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9. A solid is not considered a fluid because
a. of the fixed arrangement of its atoms and/or molecules.
b. of the heavy nature of its atoms and/or molecules.
c. its atoms and/or molecules are unusually close together.
d. Wrong! Because the atoms and/or molecules vibrate, a solid technically is a fluid.
a.
10. The level of the oceans is currently rising about 1.5 mm per year. At this rate, the
level of the ocean will rise 4.8 m in
a. 7200 years.
b. 3200 years.
c. 7.2 years.
d. 3.2 years.
b.
11. Consider two weightlifters, one of whom is 62 cm tall, and the other is 77 cm tall.
Each can raise 100 kg over her head. Which of the following statements is true?
a. The shorter weightlifter does more work in lifting the 100 kg than the taller
weightlifter.
b. The taller weightlifter does more work in lifting the 100 kg than the shorter
weightlifter.
c. Both weightlifters do exactly the same amount of work in lifting the 100 kg.
d. The weightlifter who is able to lift the 100 kg more quickly does more work.
b.
12. It takes 147 J of work to bring a 6.91-kg mass to a halt. What was the kinetic energy
of the mass just before the work started being performed?
a) 0 J
b) 6.52 J
c) 21.3 J
d) 147 J
d) From the work-energy theorem, KE = W.
13. A small car pushes a big truck up a hill; the action of the small car causes both
vehicles to accelerate up the hill at the same rate. Which of the following is true?
a) The car exerts a force on the truck greater in magnitude than the force exerted
by the truck on the car.
b) The force exerted by the car on the truck is equal in magnitude to the force
exerted by the truck on the car.
c) The truck exerts a force on the car greater in magnitude than the force the car
exerts on the truck.
d) None of the above.
b) From Newton's Third Law, for every force there is an opposing force equal in
magnitude but opposite in direction.
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14. A substance has a specific heat of 437 J/(kg·K) in the solid phase and 581 J/(kg·K) in
the liquid phase. Its melting point is at 179 K; the latent heat of fusion is 21,500 J/kg. Its
boiling point is at 681 K; the latent heat of vaporization is 189,000 J/kg. You wish to boil
off 4.2 kg of this substance that is initially at 155 K. How much heat is required?
a) 888,000 J
b) 2,210,000 J
c) 2,870,000 J
d) 2,150,000 J
d) First, the temperature of the solid must be raised to the melting point: Q = mcT =
4.2·437·(179-155) = 44,050 J; second the solid must be melted: Q = mLf = 4.2·21500 =
90,300 J; third, the liquid must have its temperature raised to the boiling point: Q = mcT
= 4.2·581·(681-179) = 1,224,980 J; last, the liquid must be vaporized: Q = mLv =
4.2·189000 = 793,800 J. Add these up and you get the total heat necessary, 2,150,000 J.
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15. A mass weighs 350 N. As it falls through the air, air resistance increases as the
speed of the object increases. Which of the following statements is true?
a) The acceleration of the mass remains g.
b) The force due to air resistance can increase until it reaches a value of 350 N.
c) The force due to air resistance can increase until it reaches 350·g.
d) None of the above.
b) the total air resistance will never be greater than mg =350 N for the object.
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16. If you had 1 moles' worth of marbles, how many would you have?
a. The answer depends upon the marbles' mass.
b. an inconveniently large number.
c. exactly 12
d. exactly 6
b.
17. An 2.0-kg object has an initial speed of 6.2 m/s. A 7.6-N force is applied in the
direction opposite to the object's initial motion. The force is applied for 4.5 seconds.
How far away is the object from its original position (i.e., at the moment the force was
first applied)?
a) 49.1 m
b) 66.4 m
c) 10.6 m
d) 27.9 m
c) F = ma  a = F/m = 7.6/2.0 = 3.8 m/s2;
0.5 · (-3.8) · 4.52 = -10.6 m.
x = x0 + v0t + ½at2 = 0.0 + 6.2 · 4.5 +
18. An astronaut in the orbiting Space Shuttle is considered weightless. What is really
taking place is that
a) the astronaut is effectively shielded from the Earth's gravity.
b) the astronaut is so far from the Earth that his weight has dwindled to zero.
c) the astronaut is accelerated by the Earth's gravity as much as the shuttle.
d) the Earth's gravity is balanced out by other celestial objects (e.g., the Moon, the
Sun, the other planets, etc.)
c) the astronaut and the space shuttle are accelerating at the same rate, so while within the
shuttle the astronaut appears weightless.
19. In science, a theory is
a. just an educated guess.
b. the same thing as a fact.
c. a synthesis of a large body of well-tested knowledge.
d. unchangeable.
c.
20. Florence Griffith-Joyner ran the 100-meter dash in 10.5 s (world
record set in 1988). She began the race stationary in the starting block and
finished traveling at 11.5 m/s. What was her average speed?
a. 11.5 m/s.
b. 1.1 m/s.
c. 9.5 m/s.
d. 0.2 m/s.
c. 100/10.5 = 9.5 (the 11.5 m/s is irrelevant in this).
21. During the Revolutionary and Civil Wars soldiers made bullets by dropping blobs of
molten lead off Natural Bridge (down by Lexington) into the creek below where they
would cool and harden into pellets. When you recreate their technique, it takes 3.7
seconds for the molten lead to hit the water below. Based on this experiment, how high
is Natural Bridge?
a. 18.1 m.
b. 36.3 m.
c. 67.1 m.
d. 134 m.
c. d = 0.5gt2 = 0.5  9.8  3.72 = 67.1 m.
22. You drop a watermelon off the top of Burruss hall. What happens to the
gravitational potential energy (PE) and kinetic energy (KE) of the watermelon as it falls?
a. both PE and KE increase.
b. both PE and KE decrease.
c. PE increases while KE decreases.
d. PE decreases while KE increases.
d.
23. For a “typical” atom, the diameter of the nucleus is on the order of 1015 m, and the
diameter of the entire atom is on the order of 1010 m. Thus, if an atomic nucleus were
about the size of a basketball (say 1 foot in diameter), the diameter of the entire atom
would be
a. 0.0000000001 feet.
b. 10,000,000,000 feet.
c. 0.00001 feet.
d. 100,000 feet.
d. The diameter of the atom is 5 orders of magnitude larger than the diameter of the
nucleus, i.e., the factor is 105. Therefore, 105  1 = 105 feet.
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24. Absolute zero of temperature is
a. 0 K.
b. 0° C.
c. the theoretical lower limit to temperature.
d. both a and c are correct.
d.
25. The momentum of a 900-kg car moving at a speed of 25 m/s is
a. 22,500 kgm/s
b. 281,000 kgm/s
c. 36 kgm/s
d. 875 kgm/s
a. p = mv = 900  25 = 22,500 kgm/s.
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26. How much heat is emitted by a sphere of radius 0.442 m with an emissivity of 0.30 at
a temperature of 295 K over the course of 1 hour (the surface area of a sphere is 4r2)?
a. 9.49 x 105 J
b. 3.27 J
c. 2.85 x 105 J
d. 79.1 J
c. Q = eAT4t = 0.30  5.67 x 10-8  4  0.4422  2954  3600 = 2.85 x 105 J.
27. A 150-g baseball strikes a 2.3-kg baseball bat. The baseball is initially travelling in
one direction at a speed of 43 m/s while the bat is travelling in the opposite direction at a
speed of 16 m/s. If, after the collision, the bat is travelling in its original direction at a
speed of 14 m/s, what is the speed of the baseball?
a. 16 m/s
b. 14 m/s
c. 12 m/s
d. 43 m/s
c. Conservation of Momentum tells us p1,initial + p2,initial = p1,final + p2,final  p1,final = p1,initial
+ p2,initial – p2,final = 0.15  43 + 2.3  (-16) – 2.3  (-14) = 1.85 = m1v1,initial  v1,initial =
1.85/0.15 = 12.3 m/s.