Test Prep Test Prep Certifications OAT Questions & Answers

• Question 211:

  A liquid is held at its freezing point and slowly allowed to solidify. Which of the following statements about this event are true?

  A. During freezing, the temperature of the material decreases.

  B. While freezing, heat is given off by the material.

  C. During freezing, heat is absorbed by the material.

  D. During freezing, the temperature of the material increases.

  Correct Answer: B

  Freezing is an exothermic event; therefore, heat must be given off. The temperature of the material remains unchanged at the freezing point during the process.

• Question 212:

  The density of helium is much lower than that of air. How does the speed of sound traveling through helium has compare to the speed of sound in air?

  A. It is faster.

  B. It is slower.

  C. It is the same speed.

  D. It cannot be determined without knowing their atomic masses.

  Correct Answer: A

  Sound travels much faster through helium than through air. Generally, the speed of sound can be calculated by speed = (k ?P / ), where k is the index of specific heats, P is pressure and is density. Since helium has a much lower density, it would have a higher speed.

• Question 213:

  Which of the following statements about electricity flowing through a circuit can be correctly derived from Ohm's law?

  A. Increasing the voltage decreases the current if the resistance remains unchanged.

  B. Increasing the current and the resistance decreases the voltage.

  C. Increasing the current increases the voltage if the resistance is uncharged.

  D. Decreasing the resistance increases the current if the voltage remains uncharged.

  Correct Answer: C

  Ohm's law is that V = IR. Answer [Increasing the current increases the...] is the only relation that holds true using this equation. If the resistance doesn't change, increasing the current on the right side must cause the voltage to also increase on the left side.

• Question 214:

  A motorcycle weighs twice as much as bicycle and is moving twice as fast. Which of the following statements is true?

  A. The motorcycle has four times as much kinetic energy as the bicycle.

  B. The motorcycle has eight times as much kinetic energy as the bicycle.

  C. The bicycle and the motorcycle have the same kinetic energy.

  D. The bicycle has four times as much kinetic energy as the motorcycle.

  Correct Answer: B

  Kinetic energy is the energy of motion and is defined as 1/2mv2. Using this equation, if you double the mass and the velocity of an object, you find KE = 1/2(2m)(2v)2 or 8 times the original KE. Therefore, the motorcycle has 8 times as much kinetic energy as the bicycle.

• Question 215:

  Which statement best explains why the work done by a gravitational force on an object does not depend on the path the object takes?

  A. Work depends on the path when there is friction. The longer the path the more energy is required to overcome friction.

  B. Gravitational fields that arise from the interaction between point masses always produce elliptical paths of motion.

  C. A falling object experiences a change in potential energy.

  D. When an object falls down the work done by gravity is positive and when an object is thrown up the work done by gravity is negative.

  Correct Answer: C

  To determine how much work is done by a gravitational force, you should calculate the change in that object's potential energy = mgh, where m = mass, g = the gravitational acceleration 9.8 m/s2 and h = height. Therefore, the work done only depends on the change in height and not on the path taken. In Answer [Work depends on the path when...], the work done by gravity doesn't have anything to do with friction, so this is not a good explanation. Friction is a separate force. Answer [When an object falls down...], although true, doesn't explain why the work doesn't depend on the path.

• Question 216:

  A bowling ball with a mass of 4 kilograms moving at a speed of 10 meters per second hits a stationary 1 kg bowling ball in a head-on elastic collision. What is the speed of the stationary ball after the collision?

  A. 0 m/s

  B. 10 m/s

  C. Less than 10 m/s, but not 0 m/s

  D. More than 10 m/s

  Correct Answer: D

  Since this is a head-on elastic collision, you could use conservation of kinetic energy and momentum to actually solve this problem. However, in this case, you only need to think through the answers to arrive at a correct conclusion. Clearly the ball after it's struck won't be going 0 m/s. And since this is an elastic collision, and it is hit by a much larger ball, it must be going faster than the larger ball was originally moving. Therefore, the ball will be moving at more than 10 m/s. If this were an inelastic collision where the balls stuck together, the ball would final velocity would be less than 10 m/s.

• Question 217:

  Which of the following demonstrations best illustrates Newton's first law?

  A. Giving a billiard ball at rest on a smooth level table a small push and letting it roll on the table.

  B. Dragging a box in a table at a constant speed by exerting a force just enough to overcome the force of friction.

  C. Trying without success to move a heavy bureau or filing cabinet on the floor.

  D. Running a current through two parallel wires.

  Correct Answer: A

  Newton's first law (inertia) says an object in motion stays in motion, and an object at rest stays at rest, unless external forces act on them. Answer [Giving a billiard ball at rest on...] is an excellent demonstration because it shows the ball at rest and in motion. At rest, the ball stays at rest until a force acts on it. When the ball is moving, there is no force acting on the ball in the direction of motion. Thus, the natural state of the ball is to be at rest or moving with a constant speed. Answer [Trying without success to...] is not a good demonstration because the force of friction is what makes it hard to move the heavy object. Answer [Dragging a box in a table at...] is a good demonstration of equilibrium and friction. Answer "running a current through wires" has nothing to do with Newton's first law.

• Question 218:

  An automobile increased its speed uniformly from 20 m/s to 30 m/s at rate 5 m/s2. During this time it traveled 50 meters. How long did it take the automobile to make this change?

  A. 5 seconds

  B. 2 seconds

  C. 10 seconds

  D. Can't be determined.

  Correct Answer: B

  The answer can be determined because the rate of acceleration is uniform. Since the acceleration is 5 m/ s2, the velocity increases by 5 m/s every second. If it starts at 20 m/s, after 1 second it will be going 25 m/

  s. After another second it will be going 30 m/s, so the total time is 2 seconds. You can also calculate this time by using the average speed. Since the object undergoes uniform acceleration, the average speed is 25 m/s. Using the distance traveled, the same result is obtained.

  t = d / v = 50 meters / 25 m/s = 2 seconds.

• Question 219:

  What property of a sound wave in air corresponds to the frequency of the sound?

  A. pitch

  B. high and low

  C. timbre

  D. overtones

  Correct Answer: A

  The frequency of a sound wave directly determines its pitch. We say the pitch of 480 Hz is higher than the pitch of 440 Hz. High and low are the words we use to describe pitch. Overtones refer to the frequencies above the fundamental frequency in a musical instrument. Two singers singing the same note at the same loudness will sound differently because their voices have different timbres.

• Question 220:

  What corresponds to the amplitude of a sound wave?

  A. loudness

  B. pressure differential of fluctuations

  C. magnitude of motion of air molecules

  D. power

  Correct Answer: B

  When a tuning fork vibrates it creates areas of condensation (higher pressure) and rarefactions (lower pressure) that propagate through the air because of the air's elasticity. The distance between the condensations or rarefactions is the wavelength of the sound. The amplitude of the sound is half the difference between the pressure of the condensation and the pressure of the rarefaction. Loudness and power are both logarithmic measures that depend on the amplitude, but are not directly proportional to it. For example, doubling the amplitude will not double the loudness or power; those quantities will increase just slightly.