Physics 111 Exam #2

53) A car is rounding a circular curve of radius r on a banked turn. As the figure shows, there are two forces acting on the car, its weight, mg, and the normal force, FN, exerted by the road. Which force, or force component, provides the centripetal force that keeps the car moving on the circular path? A) The horizontal component, FN sin, of the normal force. B) The vertical component, FN cos, of the normal force. C) The normal force, FN. D) The weight, mg, of the car.

a

63) What is the change in potential energy of an energetic 65 kg hiker who makes it from the floor of Death Valley, 85 m below sea level to the top of Mt.Whitney at 4420 m above sea level? A) 2.87x106 J B) 3.0 x106 J C) 4.4 x104 J D) 2.81 x106 J

a

64) A railroad car collides with and sticks to an identical railroad car that is initially at rest. After the collision, the kinetic energy of the system A) is the same as before. B) is half as much as before. C) is one fourth as much as before. D) is one quarter as much as before.

a

54) Which requires more work, increasing a car's speed from 40 mph to 50 mph or from 50 mph to 60 mph? A) From 40 mph to 50 mph. B) From 50 mph to 60 mph. C) It is the same in both cases. D) The answer cannot be determined.

b

55) Two identical satellites have different circular orbits shown. Which has a higher speed? A) The one in the larger orbit. B) The one in the smaller orbit. C) They have the same speed. D) The answer cannot be determined.

b

56) A hypothetical planet has a mass of one-half that of the earth and a radius of one-third that of the earth. What is the acceleration due to gravity on the planet in terms of g, the acceleration due to gravity at the surface of the earth? A) g B) 9/2 g C) 4g D) g/8 E) 2g

b

57) A uniform solid disk has mass M and radius R, and its moment of inertia about a central axis can be calculated as . If these are increased to 2M and 4R, what happens to the sphere's moment of inertia about a central axis? A) It increases by a factor of 54. B) It increases by a factor of 32. C) It increases by a factor of 16. D) It increases by a factor of 4.

b

60) The centers of a 13 kg lead ball and a 70 g lead ball are separated by 0.14 m. What is the gravitational force between them? A) 3.1 x 10-6 N B) 3.1 x 10-9 N C) 4.3 x 10-11 N D) 4.3 x 10-9 N

b

52. A nut needs to be tightened with a wrench. Which force shown below will apply the greatest torque to the nut?

c

65) What is the minimum work done by the heart to pump 160 g of blood from a person's foot to his heart 1.5 m away? A) 0.24 J B) 240 J C) 2.4 J D) 24 J

c

51) The fan blade is slowing down. What are the signs of ω and α? A) ω is positive and α is positive. B) ω is positive and α is negative. C) ω is negative and α is negative. D) ω is negative and α is positive.

d

59) You and your friend, who weighs the same as you, want to go to the top of the Eiffel Tower. Your friend takes the elevator straight up. You decide to walk up the spiral stairway, taking longer to do so. Compare the gravitational potential energy of you and your friend, after you both reach the top. A) It is impossible to tell, since the times you both took are unknown. B) It is impossible to tell, since the distances you both traveled are unknown. C) Your friend's gravitational potential energy is greater than yours, because he got to the top faster. D) Both of you have the same amount of gravitational potential energy at the top. E) Your gravitational potential energy is greater than that of your friend, because you traveled a greater distance in getting to the top.

d

62) You want to store 1,000 J of energy in an ideal spring when it is compressed by only 2.5 cm. What should be the force constant (spring constant) of this spring? A) 4.0 x 106 N/m B) 8 x 104 N/m C) 1.6 x 106 N/m D) 3.2 x 106 N/m

d

58) Two men, Joel and Jerry, push against a car that has stalled, trying unsuccessfully to get it moving. Jerry stops after 10 min, while Joel is able to push for 5.0 min longer. Compare the work they do on the car. A) Joel does 75% more work than Jerry. B) Joel does 50% more work than Jerry. C) Jerry does 50% more work than Joel. D) Joel does 25% more work than Jerry. E) Neither of them does any work.

e

61) Jill does twice as much work as Jack does and in half the time. Jill's power output is A) the same as Jack's power output. B) one-fourth as much as Jack's power output. C) one-half as much as Jack's power output. D) twice Jack's power output. E) four times Jack's power output.

e

1) In an inelastic collision involving an isolated system, the final total momentum is more than the initial momentum?

false

11) KE can be a negative value?

false

14) KE and momentum are always conserved?

false

16) If a stone is dropped with an initial gravitational potential energy of 100 J but reaches the ground with a kinetic energy of only 75 J, this is a violation of the principle of conservation of energy?

false

17) If you raise a book to a greater height you are increasing its kinetic energy?

false

18) A ball at the end of a string being swung in a vertical circle at a constant speed is not accelerating?

false

19) Every point on a rotating disk has the same linear velocity?

false

3) The following are units for impulse are kg*s/m?

false

4) Two cars are traveling at the same constant speed v. Car A is moving along a straight section of the road, while car B is rounding a circular turn. Both cars are accelerating?

false

5) A 500-kg object moving at 40 m/s and a 1000-kg object moving at 20 m/s, both have the same kinetic energy?

false

6) Increasing a car's speed from 0 mph to 30 mph or from 50 mph to 60 mph require the same amount of work?

false

8) Air bags protect people by decreasing the change in momentum suffered during crashes?

false

10) Power is the rate of doing work?

true

12) It is theoretically possible to rotate a large cylindrical space station at just the proper speed so that the people inside will experience a force that feels just like gravity?

true

13) The work done by the normal force when sliding a book across a level table is zero?

true

15) A Torque > 0 produces a change in angular momentum (τnet = ∆L)?

true

2) If an object remains at rest, then the sum of both the external torques and the external forces on the object must be zero?

true

20) A leaning car is stable if its center of mass is exactly over its pivot point?

true

7) A kangaroo has tendons in its legs that actually stretch and store some of the (elastic potential) energy in each bounce so that it can be used for another bounce.

true

9) To either stretch or compress a spring one must do positive work?

true