Physics 2 Unit 6 Review Packet

Name: ______________ Period: _________

Directions: Answer the following questions in your lab book. 1. State whether the following statements about work are true or false. Explain. a. b. c. d. e. f.

Work is a form of energy. A Joule is the standard metric unit of work. Units of work would be equivalent to a Newton times a time unit (like N-sec). A kg•m2/s2 would be a unit of work. Work is a time-based quantity; it is dependent upon how fast a force displaces an object. Superman holds a car above his head for 3 minutes to keep it from falling on a small child. This is an example of work being done. g. An upward force is applied to a bucket to lift it 5 meters above ground. This is an example of work being done. h. The force of friction acts upon a refrigerator to keep it from sliding down a sloped driveway. This is an example of work being done. i. A force acts upon an object at a 180-degree angle to the direction that it is moving. This force is doing negative work upon the object. j. An object is moving to the right. A force acts leftward upon it. This force is doing negative work.

2. State whether the following statements about energy are true or false. Explain. a. If an object is lifted vertically, then the work done on the object is equal to the change in energy that the object possesses. b. A Newton meter (N m) of work is equal to a Joule (J) of energy. c. If a 100 kg box is lifted vertically for 1 m than the energy consumed is 98 J. d. If a 100 kg box is carried horizontally for a distance of 10 m than the energy necessary to do this task is 9800 J.

3. State whether the following statements about power are true or false. Explain. a. b. c. d. e.

Power is a time-based quantity. Power is a measure of how fast work is done upon an object. A unit of power is equal to a unit of work divided by a unit of time. The standard metric unit of power is Watts multiplied by time. If person A and person B do the same job but person B does it faster, then person A and B do the same amount of work but person A takes more power to complete the job. f. To calculate the power required to do something, you multiply the force and the distance that the force is moved (in the direction of the force) and divide it by the time it took to move the force through that distance. g. A 60-kg boy runs up a 20.0 meter staircase in 15 seconds. His power is approximately 800 Watt.

6.1 Problems with Work and Energy: 4. Matt pushes a 20 kg mass 10 m across the floor with a horizontal force of 80 N. Calculate the energy required for Matt to complete this task. 5. The third floor of a house is 8 m above the street level. How much work is needed to move a 150 kg refrigerator to the third floor? 6. Stan does 176 J of work lifting himself 0.3 m. What is Stan’s mass? 7. Mike pulls a 4.5 kg sled across level snow with a force of 225 N along a rope that is 35 degrees above the horizontal. If the sled moves a distance of 65.3 m, how much work does Mike do? 8. Chris carries a 20 kg armload of wood across the lot at Home Depot for a distance of 100 m. How much work does Chris do? 9. The librarian picks up a 2.2 kg book from the floor to a height of 1.25 m. She carries is a distance of 10 m across the library and places the book on a shelf that is 0.35 m above the floor level. How much work did the librarian do? 10. Stephanie expends 11,400 J of energy to drag a wooden crate 25 m across a floor with a constant speed. The rope makes an angle of 48 degrees with the horizontal. a. How much force does the rope exert on the crate? b. What is the force of friction acting on the crate to impede its motion? ( c. What work is done by the floor through the force of friction between the floor and the crate? 6.2 Problems with Work and Power: 11. A box that weighs 575 N is lifted a distance of 20 m straight up by a cable attached to a motor. The job is done in 10 sec. What power is supplied by the motor is both watts and kilowatts? 12. A rock climber wears a 7.5 kg backpack while scaling a cliff. After 30 min, the climber is 8.2 m above her starting point. a. How much extra work did she do to raise her backpack with her on her climb? b. If the climber weighs 645 N, how much work does she do to lift herself and her backpack? c. What is the average power needed by the climber to lift herself and her backpack? 13. An electric motor provides 65 kW of power as it lifts a loaded elevator 17.5 m in 35 sec. How much force does the motor lift? 14. Willy pulls a 305N sled along a snowy path using a rope that makes a 45 degree angle with the ground. Willy pulls with a force of 42.3 N and the sled moves 16 m in 3 sec. What power does Willy produce? 15. Robin pushes a wheelbarrow by exerting a force of 145 N horizontally. Robin moves the wheelbarrow 60 m at constant speed for 25 sec. a. How much power is required for Robin to complete this task? b. If Robin completes this task with twice the speed, what is Robin’s required power output?

Physics 2 Unit 6 Review Packet

Name: ______________ Period: _________

6.3 Problems with Machines 16. Steven raises a 1500 N piano a distance of 7 m using a set of pulleys. Steven pulls in 21 m of rope. a. What is Steven’s effort force if this is an ideal machine? b. What force is used to balance the friction force is Steven actually pulls with a force of 540 N? c. What is the work output? d. What is the input work? e. What is the mechanical advantage supplied by the pulley system? 17. Clyde, a stubborn 3500-N mule, refuses to walk into the barn, so Farmer MacDonald must drag him up a 5.0-m ramp to his stall, which stands 0.50-m above ground level. a. What is the ideal mechanical advantage of the ramp? b. If Farmer MacDonald needs to exert a 450-N force on the mule to drag him up the ramp with a constant speed, what is the actual mechanical advantage of the ramp? c. What is the efficiency of the ramp? 18. The Ramseys are moving to a new town, so they have called in the ACME moving company to take care of their furniture. Donny, one of the movers, slides the Ramseys’ 2200-N china cabinet up a 6.0-mlong ramp to the moving van, which stands 1.0-m off the ground. a. What is the ideal mechanical advantage of the incline? b. If Donny must exert a 500-N force to move the china cabinet up the ramp with a constant speed, what is the actual mechanical advantage of the ramp? c. What is the efficiency of the ramp? 19. A sledgehammer is used to drive a wedge into a log to split it. When the wedge is driven 0.2 m into the log, the log is separated by a distance of 5 cm. A force of 19000 N is needed to split the log and the sledgehammer exerts a force of 9800 N. a. What is the IMA of the wedge? b. What is the MA of the wedge? c. What is the efficiency of the wedge? 20. A boy exerts a force of 225 N on a lever to raise a 1250 N rock a distance of 13 cm. If the efficiency of the lever is 88.7%, how far did the boy move his end of the lever?