1. Which of the following is true for a conservative force? A) The work done by the force is independent of the path between the initial and final positions. B) The NET work done by the force is zero when the object moves around a closed path, starting and finishing at the same point C. The work done by the force equals –ΔPE.
D. All of the above.
2. An elevator supported by a single cable descends a shaft at a constant speed. The only forces acting on the elevator are the tension in the cable and the gravitational force. Which one of the following statements is true? A) The magnitude of the work done by the tension force is greater than that done by the gravitational force. B) The magnitude of the work done by the gravitational force is greater than that done by the tension force. C) The work done by the tension force is zero joules.
D) The work done by the gravitational force is zero joules. E) The net work done by the two forces is zero joules.
3. A helicopter (m = 3250 kg) is cruising at a speed of 56.9 m/s at an altitude of 185 m. What is the total mechanical energy of the helicopter? A) 3.91 × 107 J
D) 6.91 × 107 J
B) 5.26 × 107 J
E) 1.12 × 107 J
C) 2.27 × 108 J
4. The power needed to accelerate a projectile from rest to its launch speed v in a time t is 50 W. How much power is needed to accelerate the same projectile from rest to a launch speed of 3v in a time of 3t ? Assume no change in height before launch.
| A. 50 W B. 100 W C. 150 W D. 300 W E. 400 W
| The next 2 questions refer to the diagram below:
A string is tied to a doorknob 0.72 m from the hinge as illustrated in the figure. At the instant shown, the force applied to the string (F) is 5.0 N. This is a top-down (bird’s eye) view.
5. What is the line of action in this diagram?
A) The dashed line opposite the 57° angle
B) The solid line opposite the 33° angle.
C) The top of the door
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