Ch 9 Energy - Fenger Academy High School



Ch 9 Work, Power & Energy

Work and Power Classwork

Solve the following questions from the textbook using the formula below

Work = Force * Distance

Power = Work / Time

Power = (Force * Distance) / Time

1. Work is required to lift a barbell. How many times more work is required to lift the barbell 3 times as high?

2. Which requires more work, lifting a 10-kg load a vertical distance of 2 m or lifting a 5-kg load a vertical distance of 4 m?

3. How many Joules of work are done on an object when a force of 10N pushes it a distance of 10m?

4. How much power is required to do 100J of work on an object in a time of 0.5 s? How much work is required if the same work is done in 1 s?

5. Calculate the work done when a 20-N force pushes a cart 3.5m.

6. Calculate the work done in lifting a 500-N barbell 2.2 m above the floor.

7. Calculate the Watts of power expended when a force of 1 N moves a book 2 m in a time interval of 1 s.

8. Calculate the power expended when a 20-N force pushes a cart 3.5 m in a time of 0.5 s.

Work and Power Homework

SHOW YOUR WORK AND REMEMBER YOUR UNITS

1. How much work is done when an 8 N force moves a block 7m? [2 Points]

2. Eva applies 40N force to move her bookcase 3m, how much work did Eva do? [2 Pts]

3. How far will 490 J of work raise a block weighing 7 N? [3 Points]

4. Sheila did 110 J of work to move a chair 2 m to the right. How much force did Sheila use to move the chair? [3 Points]

5. Which is more work, pushing with 115 N over 15m or lifting 20N over 10 m? [2 Pts]

6. How much power does it take to do 500 J of work in 10 sec? [2 Points]

7. How much power does it take to lift 250 N, 40 m high in 2 seconds? [3 Points]

8. If it takes 20 N to move a box, how much power will be needed to move the box a distance of 5 meters in 5 seconds? [3 Points]

Kinetic Energy = Work done = ½ mass * velocity2

Potential Energy = Work done = mass * gravity * height

Kinetic & Potential Energy textbook problems for classwork.

1. What are the two main forms of mechanical energy?

2. a. If you do 100J of work to elevate a bucket of water, what is its gravitational potential energy relative to its starting position?

b. What would the grav potential energy be if the bucket were raised twice as high?

3. Four carts A,B, C & D of different masses and speeds run up short inclines. Rank the carts by kinetic energy

A. 1-kg, 4 m/s B. 2-kg, 3 m/s C. 3-kg, 2m/s D. 4-kg, 1m/s

4. How many Joules of work of potential energy does a 1-kg book gain when it is elevated 4m? When it is elevated 8m?

5. Calculate the increase in potential energy when a 20-kg block of ice is lifted a vertical distance of 2m.

6. Calculate the kinetic energy a 1-kg book has when tossed across the room at a speed of 2 m/s.

7. How much work is required to increase the kinetic energy of a car by 5000J?

8. What change of kinetic energy does an air-plane experience on takeoff if it is moved a distance of 500m by a sustained net force of 5000N?

Mechanical Advantage = Output force / Input Force

Efficiency = Useful output work / Work Input

Machines and Efficiency textbook problems for classwork

1. In what 2 ways can a machine alter an input force?

2. In what way is the machine subject to the law of energy conservation? Is it possible for a machine to multiply energy?

3. What is the efficiency of a machine that requires 100 J of energy to do 35 J of work?

4. What is the efficiency of the bicycle when a cyclist puts in 1000 W of power to a bicycle which outputs power the rate of 100 W?

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