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Chapter 5

This document defines key concepts related to work, energy, and power. It defines work, gravitational potential energy, elastic potential energy, and kinetic energy. It states the principle of conservation of energy and the work-energy theorem. It defines average power and describes how to derive power. It also defines mechanical efficiency. The document provides examples of calculating work, energy, power, and efficiency in various physical situations.

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Shirah Cool
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114 views3 pages

Chapter 5

This document defines key concepts related to work, energy, and power. It defines work, gravitational potential energy, elastic potential energy, and kinetic energy. It states the principle of conservation of energy and the work-energy theorem. It defines average power and describes how to derive power. It also defines mechanical efficiency. The document provides examples of calculating work, energy, power, and efficiency in various physical situations.

Uploaded by

Shirah Cool
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
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CHAPTER 5: WORK, ENERGY AND POWER 15

RISE @ PHYSICS

1. Define Work Done

2. Define Gravitational Potential


Energy

3. Define Elastic Potential Energy

4. Define Kinetic Energy

5. State the principle of


conservation of energy

6. State work-energy theorem

7. Define average power

8. Derive Power

9. Define mechanical efficiency

15 | P a g e
CHAPTER 5: WORK, ENERGY AND POWER 16
RISE @ PHYSICS

1. The variation of force that acts on an object in the direction of x with the displacement x
is shown in the graph below. Determine the work done by the force to move the object to
a displacement of 8.0 m.

F/N

x/m
2 6 8
Answer: 24 J

2. A man lifts an object of mass 1.5 kg vertically upwards through a distance of 2.0 m with
constant speed. Determine

a. the work done by the man


b. the work done by the gravitational force
c. the total work done by the two forces

Answer: (a) 29.43 J; (b) ‒29.43 J; (c) 0 J

3. A spring is stretched from 12 cm to 14 cm, find the amount of energy stored in the
spring. Given spring constant = 200 N m-1.

Answer: 4×10-2 J

4. A trolley of mass 10 kg moves with a velocity of 15 m s-1. Find the kinetic energy of the
trolley.

Answer: 1125 J

5. Find the amount of potential energy in object A if its mass is 5 kg at position 200 cm
from ground.

Answer: 98.1 J

6. A bullet of mass 1.5 g is fired with a speed of 124 m s-1 crashes through a concrete of
thickness 0.60 m. Its speed is 92 m s-1 after passing through the concrete. Determine

a. the work done by the bullet


b. the retarding force that acts on the bullet

Answer: (a) ‒5.18 J ; (b) 8.64 N

16 | P a g e
CHAPTER 5: WORK, ENERGY AND POWER 17
RISE @ PHYSICS

7. In a diving competition, a competitor leaps off a 10 m high board with initial velocity of
0.80 m s-1. After completing 2 twists, he hits the water with little splash of water.

a. Calculate the velocity of the competitor when he hits the water.


b. State the assumption for your calculation above.

Answer: (a) 14 m s-1 ; (b) u think

8. A block of mass 2.0 kg moves with a velocity v towards a spring as shown in figure
below. v

The block compresses the spring by 2.0 cm. Given that the force constant of the spring
is 1000 N m-1. Determine the velocity of the block if

a. the surface is smooth


b. the surface is rough and the frictional force between the block and the surface is
3.0 N

Answer: (a) 0.45 m s-1 ; (b) 0.51 m s-1

9. A boat of mass 850 kg moves with a uniform velocity of 2.5 m s-1 on the surface of the
sea. If the thrust required to overcome frictional force is 3200 N, determine the average
power of the boat.

Answer: 8000 W

10. An electric motor is used to lift a load of 120 kg. The power of the motor is 1500 W. If
the efficiency of the motor is 60%, calculate the time taken to lift the load through a
height of 5.0 m.

Answer: 6.54 s

17 | P a g e

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