Assignment 10.0 – Vocabulary

 

Define each of the following terms.

 

1.                  Work

 

 

 

2.                  Energy

 

 

 

3.                  Kinetic Energy

 

 

 

4.                  Work-Energy Theorem

 

 

 

5.                  Joule

 

 

 

6.                  Power

 

 

 

7.                  Watt

 

 

 

8.                  Machine

 

 

 

9.                  Effort Force

 

 

 

10.              Resistance Force

 

 

 


 

 

11.              Mechanical Advantage

 

 

 

12.              Ideal Mechanical Advantage

 

 

 

13.              Efficiency

 

 


 

 

Assignment 10.1 – Energy & Work

 

Short Answer: Answer each question in the space provided. Write or print clearly.  IF I CAN’T READ IT, IT’S WRONG.

 

1.                  Suppose a satellite revolves around Earth in a circular orbit. Does Earth’s gravity do any work on the satellite?

 

 

 

 

2.                  An object slides at constant speed on a frictionless surface. What forces act on the object? What work is done by each force?

 

 

 

 

3.                  Define work and power.

 

 

 

 

 

 

4.                  What is a watt equivalent to in term of kilograms, meters, and seconds?

 

 

 

 

5.                  Which required more work, carrying a 420 N backpack up a 200 m high hill or carrying a 210 N backpack up a 400 m high hill?

 

 

 

 

6.                  You slowly lift a box of books from the floor and put it on a table. Earth’s gravity exerts a force, magnitude mg downward, and you exert a force, magnitude mg upward. The two forces have equal magnitudes and opposite directions. It appears that no work is done, but you know that you did work. Explain what work was done.

 

 

 


 

 

7.                  You have an after school job carrying cartons of new copy paper up a flight of stairs, and then carrying recycled paper back down the stairs. The mass of the paper does not change. Your physics teacher says that you do not work all day, so you should not be paid.

A)                In what sense is the physics teacher correct?

 

 

 

 

B)                What arrangement of payments might you make to ensure that are properly compensated?

 

 

 

 

8.                  You carry the cartons of copy paper down the stairs and then along a 15 m long hallway. Are you doing work while carrying the paper down the hallway? Explain.

 

 

 

 

9.                  Two people of the same mass climb the same flight of stairs. The first person climbs the stairs in 25 s; the second person does so in 35 s.

A)                Which person does more work? Explain your answer.

 

 

 

 

B)                Which person produces more power? Explain your answer.

 

 

 

 

Problems: Solve each of the following problems. Show all work. Circle your answer expressed with the correct number of significant figures and units.

 

10.              The third floor of a house is 8 m above street level. How much work is needed to move a 150 kg refrigerator to the third floor?


 

 

11.              Hal does 176 J of work lifting himself 0.300 m. What is Hal’s mass?

 

 

 

 

 

 

 

 

 

12.              To keep a car traveling at constant velocity, a 551 N force is needed to balance frictional forces. How much work is done against friction by the car as it travels from Columbus to Cincinnati, a distance of 161 km?

 

 

 

 

 

 

 

 

 

13.              A cyclist exerts a force of 15.0 N as he rides a bike 251 m in 30.0 s. How much power does the cyclist develop?

 

 

 

 

 

 

 

 

 

14.              A student librarian lifts a 2.2 kg book from the floor to a height of 1.25 m. He carries the book 8.0 m to the stacks and places the book on a shelf that is 0.35 m above the floor. How much work does he do on the book?


 

 

15.              A force of 300.0 N is used to push a 145 kg mass 30.0 m horizontally in 3.00 s.

A)                Calculate the work done on the mass.

 

 

 

 

 

 

 

 

 

B)                Calculate the power developed.

 

 

 

 

 

 

 

 

 

16.              Shawna is pushing a lawn mower with a force of 88.0 N along a handle that makes an angle of 41.0º with the horizontal. How much work is done by Shawna in moving the lawn mower 1.2 km to mow the yard?

 

 

 

 

 

 

 

 

 

 

17.              A 120 kg lawn tractor goes up a 21º incline that is 12.0 m long in 2.5 s. Calculate the power that is developed by the lawn tractor.


 

 

18.              Dan pulls a 4.5 kg sled across level snow with a force of 225 N on a rope that is 35.0º above the horizontal. If the sled moves a distance of 65.3 m, how much work does Dan do?

 

 

 

 

 

 

 

 

 

19.              A 12.0 m long conveyor belt, inclined at 30.0º is used to transport bundles of newspapers from the mail room up to the cargo bay to be loaded onto delivery trucks. Each newspaper has a mass of 1.0 kg and there are 24 newspapers per bundle. Determine the power that the conveyor develops if it delivers 15 bundles per minute.

 


 

 


 

 

Assignment 10.2 – Machines

 

 

Short Answer: Answer each question in the space provided. Write or print clearly.  IF I CAN’T READ IT, IT’S WRONG.

 

1.                  Is it possible to get more work out of a machine than you put into it?

 

 

 

 

2.                  Explain how the pedals of a bicycle are a simple machine.

 

 

 

 

3.                  How can you increase the ideal mechanical advantage of a machine?

 

 

 

 

4.                  How can you increase the mechanical advantage of a wedge without changing its ideal mechanical advantage?

 

 

 

 

 


 

 

Problems: Solve each of the following problems. Show all work. Circle your answer expressed with the correct number of significant figures and units.

 

5.                  Tim raises a 1200 N piano a distance of 5.00 m using a set of pulleys. He pulls in 20.0 m of rope.

A)                How much effort force would Tim apply if this were an ideal machine?

 

 

 

 

 

 

 

B)                What force is used to balance the friction force if the actual effort is 340 N?

 

 

 

 

 

 

 

C)                What is the output work?

 

 

 

 

 

 

 

D)                What is the input work?

 

 

 

 

 

 

 

E)                 What is the mechanical advantage?


 

 

6.                  Because there is very little friction, the lever is an extremely efficient simple machine. Using a 90.0 percent efficient lever, what input work is required to lift an 18.0 kg mass through a distance of 0.50 m?

 

 

 

 

 

 

 

 

 

 

7.                  What work is required to lift a 215 kg mass a distance of 5.65 m, using a machine that is 72.5% efficient?

 

 

 

 

 

 

 

 

 

 

8.                  ch10resource_assessment8The ramp in the figure to the right is 18 m long and 4.5 m high.

A)                What force, parallel to the ramp (FA) is required to slide a 25 kg box at constant speed to the top of the ramp if friction is disregarded?

 

 

 

 

 

 

B)                What is the IMA of the ramp?

 

 

 

 

 

 


 

 

C)                What is the real MA of the ramp if a parallel force of 75 N is actually required?

 

 

 

 

 

 

 

D)                What is the efficiency of the ramp if a parallel force of 75 N is actually required?

 

 

 

 

 

 

9.                  ch10resource_assessment9Lisa pedals a bicycle with a gear radius of 5.00 cm and a wheel radius of 38.6 cm as show in the figure to the right. If the wheel revolves once, what is the length of the change that was used?

 

 

 

 

 

 

 

 

10.               A motor with an efficiency of 88% operates a crane with an efficiency of 42%. If the power reupplied to the motor is 5.5 kW, with what constant speed does the crane lift a 410 kg crate of machine parts?