[ Questions #1#14  Questions #15#28  Questions #29#42  Questions #43#56  Questions #57#66 ] [ #1  #2  #3  #4  #5  #6  #7  #8  #9  #10  #11  #12  #13  #14 ] 
1. An object is raised above the ground gaining a certain amount of potential energy. If the same object is raised twice as high it gains __________.
Answer and Explanation: 
Answer: B The potential energy of an object is directly proportional to the height of the object above the ground (or some other arbitrary "zerolevel") in accordance with the equation If the h in the equation is doubled (the object is raised twice as high), then the PE is doubled as well. 
Link to More Information About ... 

2. When an object is lifted 10 meters, it gains a certain amount of potential energy. If the same object is lifted 20 meters, its potential energy is _____.
a. less 
b. the same 
c. twice as much 
d. four times as much 
e. more than 4 time as much 
Answer and Explanation: 
Answer: C The potential energy of an object is directly proportional to the height of the object above the ground (or some other arbitrary "zerolevel") in accordance with the equation If the h in the equation is doubled (say from 10 m to 20 m), then the PE is doubled as well. 
Link to More Information About ... 

3. A 1000 kg car and a 2000 kg car are hoisted the same distance at constant speed in a gas station. Raising the more massive car requires ____________.
a. less work 
b. as much work 
c. twice as much work. 
d. four times as much work 
e. more than 4 times as much work 
Answer and Explanation: 
Answer: C The amount of work done by a force to displace an object is found from the equation The force required to raise the car at constant speed is equivalent to the weight (m*g) of the car. Since the 2000kg car weight 2X as much as the 1000kg car, it would require twice as much work to lift it the same distance. 
Link to More Information About ... 

4. An object that has kinetic energy must be ____________.
a. moving 
b. falling 
c. at an elevated position 
d. at rest 
e. none of these 
Answer and Explanation: 
Answer: A Pay attention to the keywords "must be." Kinetic energy is the energy of motion and an object must be moving if it has kinetic energy. The object could be falling and could be at an elevated position; the object must not be at rest if it has kinetic energy. 
Link to More Information About ... 

5. An object that has potential energy has this energy because of its _____________.
a. speed 
b. acceleration 
c. momentum 
d. position 
e. none of these 
Answer and Explanation: 
Answer: D Potential energy is the energy of position and any object which has potential energy owes this PE to the fact that it has some given position other than the socalled "zerolevel position." 
Link to More Information About ... 

6. An arrow is drawn so that it has 40 J of potential energy. When fired horizontally, the arrow will have a kinetic energy of ________.
a. less than 40 J 
b. more than 40 J 
c. 40 J 
Answer and Explanation: 
Answer: C A drawn arrow has 40 J of stored energy due to the stretch of the bow and string. When released, this energy is converted into kinetic energy such that the arrow will have 40 J of kinetic energy upon being fired. Of course, this assumes no energy is lost to air resistance, friction or any other external forces and that the arrow is shot horizontally. 
Link to More Information About ... 

7. A 2 kg mass is held 4 m above the ground. What is the approximate potential energy of the mass with respect to the ground?
a. 20 J 
b. 40 J 
c. 60 J 
d. 80 J 
e. none of these 
Answer and Explanation: 
Answer: D The potential energy of an object is found from the equation where m is mass, h is height, and g=10 m/s/s (approx.). Plugging and chugging into this equation yields PE=(2 kg)*(10 m/s/s)*(4 m) = 80 J. 
Link to More Information About ... 

8. A 2 kg mass has 40 J of potential energy with respect to the ground. Approximately how far is it located above the ground?
a. 1 m 
b. 2 m 
c. 3 m 
d. 4 m 
e. none of these 
Answer and Explanation: 
Answer: B The potential energy of an object is related to its height by the equation where m is mass, h is height, and g=10 m/s/s (approx.). Plugging and chugging into this equation yields 40 J = (2 kg)*(10 m/s/s)*(h); rearranging and solving for h yields an answer of 2 m. 
Link to More Information About ... 

9. A ball is projected into the air with 100 J of kinetic energy which is transformed to gravitational potential energy at the top of its trajectory. When it returns to its original level after encountering air resistance, its kinetic energy is ____________.
a. less than 100 J 
b. 100 J 
c. more than 100 J 
d. not enough information given 
Answer and Explanation: 
Answer: A During any given motion, if external forces do work upon the object, then the total mechanical energy will be changed. If external forces do negative work (i.e., F*d*cos(Theta) is a negative number), then the final TME is less than the initial TME. In this case, air resistance does negative work to remove energy from the system. Thus, when the ball returns to its original height, their is less TME than immediately after it was thrown. At this same starting height, the PE is the same as before. The reduction in TME is made up for by the fact that the kinetic energy has been reduced; the final KE is less than the initial KE. 
Link to More Information About ... 

10. A woman lifts a box from the floor. She then carries with constant speed to the other side of the room, where she puts the box down. How much work does she do on the box while walking across the floor at constant speed?
a. zero J 
b. more than zero J 
c. more information needed to determine 
Answer and Explanation: 
Answer: A For any given situation, the work done by a force can be calculated using the equation where F is the force doing the work, d is the displacment of the object, and Theta is the angle between the force and the displacement. In this specific situation, the woman is applying an upward force on the box (she is carrying it) and the displacement of the box is horizontal. The angle between the force (vertical) and the displacement (upward) vectors is 90 degrees. Since the cosine of 90degrees is 0, the woman does not do any work upon the box. A detailed discussion of a similar situation (the waiter and the tray of food) can be found at The Physics Classroom. 
Link to More Information About ... 

11. A car moving at 50 km/hr skids 20 m with locked brakes. How far will the car skid with locked brakes if it is traveling at 150 km/hr?
a. 20 m 
b. 60 m. 
c. 90 m 
d. 120 m 
e. 180 m 
Answer and Explanation: 
Answer: E When a car skids to a stop, the work done by friction upon the car is equal to the change in kinetic energy of the car. Work is directly proportional to the displacement of the car (skidding distance) and the kinetic energy is directly related to the square of the speed (KE=0.5*m*v^2). For this reason, the skidding distance is directly proportional to the square of the speed. So if the speeds is tripled from 50 km/hr to 150 km/hr, then the stopping distance is increased by a factor of 9 (from 20 m to 9*20 m; or 180 m). A detailed discussion of the distancespeed squared relationship can be found at The Physics Classroom. 
Link to More Information About ... 

12. Which has greater kinetic energy, a car traveling at 30 km/hr or a halfasmassive car traveling at 60 km/hr?
a. the 30 km/hr car 
b. the 60 km/hr car 
c. both have the same kinetic energy 
Answer and Explanation: 

Answer: B This problem is complicated by the fact that no mass is given for the two cars; only the ratio of mass is known. The complication can be resolved in one of two ways: 1) make up a mass for each car  such as 10 kg and 5 kg, or 2) assign m as the mass of one of the cars and (1/2)m as the mass of the second car. Then use the kinetic equation and plug and chug. The mass can then be determined for each car and compared. Using the second method yields the following results for the two cars:

Link to More Information About ... 

13. A diver who weighs 500 N steps off a diving board that is 10 m above the water. The diver hits the water with kinetic energy of ___________.
a. 10 J 
b. 500 J 
c. 510 J 
d. 5000 J 
e. more than 5000 J. 
Answer and Explanation: 
Answer: D The use of the workenergy theorem and a simple analysis will yield the solution to this problem. Initially, there is only PE; finally, there is only KE. Assuming negligible air resistance, the kinetic energy of the diver upon hitting the water is equal to the potential energy of the diver on top of the board. m*g*h_{i} = KE_{f} Substituting 500 N for m*g (500 N is the weight of the diver, not the mass) and 10 m for h will yield the answer of 5000 J. 
Link to More Information About ... 

[ #1  #2  #3  #4  #5  #6  #7  #8  #9  #10  #11  #12  #13  #14 ]
14. A 2500 N pile driver ram falls 10 m and drives a post 0.1 m into the ground. The average impact force on the ram is _________.
a. 2500 N 
b. 25000 N 
c. 250,000 N 
d. 2,500,000 N 
Answer and Explanation: 
Answer: C The use of the workenergy theorem and a simple analysis will yield the solution to this problem. Initially, there is only PE; finally, there is neither PE nor KE; external work has been done by an applied force upon the pile driver. Assuming negligible air resistance, the kinetic energy of the diver upon hitting the water is equal to the potential energy of the diver on top of the board. PE_{i} =  W_{ext} m*g*h_{i} =  F*d*cos(Theta) Substituting 2500 N for m*g (2500 N is the weight of the driver, not the mass); 10 m for h; 0.1 m for the displacement of the driver as caused by the upward applied force exerted by the ram; and 90 degrees for Theta (the angle between the applied force and the displacement of the ram) will yield the answer of 250000 N for F. 
Link to More Information About ... 

[ #1  #2  #3  #4  #5  #6  #7  #8  #9  #10  #11  #12  #13  #14 ]
Navigate to Answers for: [ Questions #1#14  Questions #15#28  Questions #29#42  Questions #43#56  Questions #57#66 ] 



[ Course Calendars  Makeup Labs  Physics Classroom  Multimedia Physics Studios  The Quiz Room  Packet Solutions (P163)  Extra Credit  Reviews  P173 Internet Problems  ChemPhys Internet Problems  P163 Projects  The Refrigerator  Miscellaneous Help  EMail Physics Teachers  Conceptual Physics  Physics 163  Physics 173  Chem  Phys  AP Physics  GBS Physics Home Page  GBS Science Home Page ]
Comments and suggestions can be sent by email to Tom Henderson.
This page last updated on December 13, 1999.