Practice Test
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
D) The circumference of the circle made by swinging the door open.
6. What is the magnitude of the torque on the door?
A) 3.60 N × m D) 4.19 N × m
B) 3.02 N × m E) 0.60 N × m
C) 1.96 N × m
The next 3 questions refer to the following situation: A 90-kg man balances the boy on a uniform teeter-totter of mass 20 kg as shown.
7. Where is the center of gravity of the teeter totter in this situation?
A. At the fulcrum
B. Between the man and the fulcrum
C. Between the boy and fulcrum
D. Depends on the weight of the boy
8. What is the mass of the boy?
A) 10 kg B) 15 kg C. 20 kg D) 22.5 kg E. 25 kg
9. What is the force does the fulcrum exert on the teeter-totter?
A) 1225 N B) 1029 N C. 196 N D. 882 N E. 0 N
10. A constant force of 25 N is applied as shown to a block which undergoes a displacement of 7.5 m to the right along a frictionless surface while the force acts. What is the work done by the force? This is a side view.
A) zero joules B) +94 J C) –94 J D) +162 J E) –162 J
END OF SCANTRON SECTION
11. A horizontal, 10-m plank weighs 100 N. It rests on two supports that are placed 1.0 m from each end as shown in the figure.
a. Draw an extended free body diagram of this situation, showing all forces on the object of interest. You can use the picture and just add the forces if you wish.
How close to one end can an 800-N person stand without causing the plank to tip?
12. Sam, whose mass is75.0 kg, takes off from rest down a down a 10.0° incline on his new, jet-powered skis, which provide a thrust force of 200.0 N. The hill is 288 m long. The frictional coefficient between his skis and the snow is 0.165 Assume the force due to the jet skis is parallel to the slope.
a. Draw a free-body diagram showing all forces on the skier, with appropriate axes and use this to calculate the net work done by all non-conservative forces on the skier after being towed 100 meters.
b. What is his speed at the bottom of the hill? [Hint: the height of the hill can be determined by using the sine function if you know the length of the hill].
13. Starting from rest, workers use a rope to pull an 85.0 kg block across the floor. The rope has a tension of 240.0 N and makes a 20.0-degree angle with the floor. The coefficient of kinetic friction between floor and block is 0.200, and the block moves a distance of 8.00 m.
a) Draw a free body diagram showing all forces on the block.
b) How fast is the block moving after being pulled a distance of 8.00 m?
14. A uniform plank of weight w is supported by the pivot shown below. The bowl of catfood at the left end of the plate also has weight w. The 2 cats weight twice as much, 2w. The distance, d, is 1.0 m.
a. Draw and label force vectors (in terms of w) at each point where a force acts on the beam. The length of the each vector should indicate its relative magnitude, compared to the other forces.
b. Is the beam in equilibrium? You must EXPLAIN your answer in words (although you can use an equation too).
15. The ladder leans against a frictionless wall. The coefficient of static friction between the ladder and the wall is 0.40.
a. Draw an extended free body diagram of this situation, showing all forces on the object of interest. You can use the picture and just add the forces if you wish.
b. What is the minimum angle the ladder can make with the floor without slipping? (It’s not 60°, so don’t use that in your calculations)