Interactive Quiz #2

This self-graded quiz consists of 10 questions (Part A of the 1996/97 Test 2). Answers are entered by clicking the option button corresponding to your selection. The quiz is graded by clicking the "Grade Quiz" button at the end of the quiz. Correct answers are found through hypertext links located at the end of the quiz.

1. A stunt person jumps from the roof of a tall building, but no injury occurs because the person lands on a large, air-filled bag. Which of the following statements best explains why no injury occurs?
    (A) The bag provides the necessary force to break the person's fall.
    (B) The bag increases the amount of time during which the momentum is changing, and therefore reduces the average force on the person.
    (C) The bag reduces the impulse acting on the person.
    (D) The bag increases the amount of time the force acts on the person, and therefore reduces the person's change in momentum.
    (E) The bag decreases the amount of time during which the momentum change occurs, and therefore reduces the average force on the person.
2. Consider a rigid wheel that is rotating with a decreasing angular velocity about a fixed axis. Point A is located on the rim of the wheel and point B is halfway between the rim and the axis. Which of the following statements is true concerning this situation?
    (A) Both points have the same centripetal acceleration.
    (B) Both points have the same tangential acceleration.
    (C) The angular velocity of A is greater than that of B.
    (D) Both points have the same instantaneous angular velocity.
    (E) Each second, A turns through a greater angle than B.
3. A rectangular, steel block of mass M will be in static equilibrium only if
    (A) the net external force acting on the block is zero.
    (B) the net external torque acting on the block is zero.
    (C) the net external force and the net external torque both equal zero.
    (D) neither the net external force nor the net external torque equal zero.
    (E) the net external force produces a non-zero, net external torque.
4. Which of the following statements best describes the state of motion of a rigid object acted upon by a constant net torque?
    (A) constant angular velocity
    (B) constant angular momentum
    (C) constant rotational kinetic energy
    (D) constant angular acceleration
    (E) at rest
5. A boy and a girl are riding on a merry-go-round that is turning. The boy is twice as far as the girl from the merry-go-round's centre. If the boy and girl are of equal mass, which statement is true regarding the boy's moment of inertia with respect to the axis of rotation?
    (A) Iboy = 1/4 Igirl
    (B) Iboy = 1/2 Igirl
    (C) Iboy = Igirl
    (D) Iboy = 2 Igirl
    (E) Iboy = 4 Igirl
6. Stars originate as large bodies of slowly rotating gas. These clumps of gas slowly decrease in size due to internal gravitational attraction. The angular velocity of a star increases as it shrinks because
    (A) heat and light energy are conserved.
    (B) linear momentum is conserved.
    (C) mechanical energy is conserved.
    (D) mass is conserved.
    (E) angular momentum is conserved.
7. Which statement is true concerning an object executing simple harmonic motion?
    (A) Its velocity is never zero.
    (B) Its acceleration is never zero.
    (C) Its velocity and acceleration can be zero simultaneously.
    (D) Its velocity is zero when its acceleration is a maximum.
    (E) Its maximum acceleration has the same magnitude as its maximum velocity.
8. Two dams are identical with the exception that the water reservoir behind dam A extends twice the distance behind it as dam B. The depth of water is the same in both cases. Which of the following statements regarding these dams is correct?
    (A) The force exerted by the water on dam A is greater than that on dam B.
    (B) The force exerted by the water on dam B is greater than that on dam A.
    (C) Dam A is more likely to collapse if the water level in both dams rises by 1 metre.
    (D) Dam B is more likely to collapse if the water level in both dams rises by 1 metre.
    (E) The horizontal distance of the water behind the dams does not determine the force on them.
9. A piece of wood and an ingot of iron have equal volumes. They are both placed in a swimming pool filled with water. The wood floats on the surface and the iron sinks to the bottom. Which one of the following statements is correct concerning the buoyant forces acting on the two objects?
    (A) The floating wood has a greater buoyant force on it since it is fully supported by the water.
    (B) The submerged iron has a greater buoyant force on it.
    (C) They both have the same buoyant force acting on them.
    (D) They will have different buoyant forces acting on them but it is impossible to tell which is greater without knowing the actual weights of the two objects.
    (E) The floating wood will have a greater buoyant force on it but only if its density is greater than that of water.
10. A pipeline is replaced with one of equal length and twice the radius. If the same pressure differential is applied across the new pipeline, and the same liquid is transported, the new volume flow rate, Q2, expressed in terms of the old volume flow rate, Q1, is:
    (A) Q2 = 2 Q1
    (B) Q2 = 4 Q1
    (C) Q2 = 6 Q1
    (D) Q2 = 8 Q1
    (E) Q2 = 16 Q1
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Correct Answers

#1, #2, #3, #4, #5, #6, #7, #8, #9, #10
1. A stunt person jumps from the roof of a tall building, but no injury occurs because the person lands on a large, air-filled bag. Which of the following statements best explains why no injury occurs?
    (B) The bag increases the amount of time during which the momentum is changing, and therefore reduces the average force on the person.
Section 7.1 of the text. Average force equals the change in momentum divided by the time interval over which the change occurs.
2. Consider a rigid wheel that is rotating with a decreasing angular velocity about a fixed axis. Point A is located on the rim of the wheel and point B is halfway between the rim and the axis. Which of the following statements is true concerning this situation?
    (D) Both points have the same instantaneous angular velocity.
Sections 8.1, 8.2, 8.4, and 8.5 of the text. For rotational motion of a rigid body, angular quantities are the same throughout, but tangential and centripetal accelerations depend on distance from axis of rotation.
3. A rectangular, steel block of mass M will be in static equilibrium only if
    (C) the net external force and the net external torque both equal zero.
Section 9.2 of text.
4. Which of the following statements best describes the state of motion of a rigid object acted upon by a constant net torque?
    (D) constant angular acceleration
Section 9.4 of the text. A net torque causes an angular acceleration.
5. A boy and a girl are riding on a merry-go-round that is turning. The boy is twice as far as the girl from the merry-go-round's centre. If the boy and girl are of equal mass, which statement is true regarding the boy's moment of inertia with respect to the axis of rotation?
    (E) Iboy = 4 Igirl
Section 9.4 of text. I = sum of miri2. For two 'point' objects of equal mass, moment of inertia depends on the square of the distance of the object from the axis of rotation.
6. Stars originate as large bodies of slowly rotating gas. These clumps of gas slowly decrease in size due to internal gravitational attraction. The angular velocity of a star increases as it shrinks because
    (E) angular momentum is conserved.
Section 9.6 of text. Since the external torque is 0, angular momentum, L, is conserved. Since the moment of inertia decreases as the clump of gas decreases in size, the angular velocity will increase to keep L constant.
7. Which statement is true concerning an object executing simple harmonic motion?
    (D) Its velocity is zero when its acceleration is a maximum.
Section 10.4 of text. Acceleration is maximum at maximum displacement, where velocity is zero.
8. Two dams are identical with the exception that the water reservoir behind dam A extends twice the distance behind it as dam B. The depth of water is the same in both cases. Which of the following statements regarding these dams is correct?
    (E) The horizontal distance of the water behind the dams does not determine the force on them.
Sections 11.2 and 11.3 of text. The force per unit area due to the pressure of the water acts perpendicularly to the dam and depends only on the depth of water.
9. A piece of wood and an ingot of iron have equal volumes. They are both placed in a swimming pool filled with water. The wood floats on the surface and the iron sinks to the bottom. Which one of the following statements is correct concerning the buoyant forces acting on the two objects?
    (B) The submerged iron has a greater buoyant force on it.
Section 11.6. Since both objects have the same volume, the submerged iron displaces more water than the floating wood, and therefore experiences a larger buoyant force.
10. A pipeline is replaced with one of equal length and twice the radius. If the same pressure differential is applied across the new pipeline, and the same liquid is transported, the new volume flow rate, Q2, expressed in terms of the old volume flow rate, Q1, is:
    (E) Q2 = 16 Q1
Section 11.11 of text. Since a pressure differential is applied, the liquid must be viscous. From Poisseuille's Law, with all else being equal, Q varies as R4.

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