Problem Based on ‘Work and Energy’

1. A force of 10 N is acting on object by which object moves 5 meter. Find the work done by object ?

Sol. Given F = 10 N s = 5 m

We know that

W = F * s

= 10 * 5

W = 50 N m or 50 J

2. A force of 50 N is acting on object by which object moves 50 meter. Find the work done by object ?

Sol. Given F = 50 N s = 50 m

We know that

W = F * s

= 50 * 50

W = 2500 N m or 2500 J

3. A man lifts a mass of 50 Kg for a height of 3 m from the floor. Calculate the work done by man ? ( Take g = 10 m / sec^2 )

Sol. Given m = 50 kg s = 3 m

We know that

W = F * s ….(1)

We also know that

F = m g

Put this value in Equation (1)

W = m g s

W = 50 * 10 * 3

W = 1500 J

4. A man lifts a mass of 100 Kg for a height of 5 m from the floor. Calculate the work done by man ? ( Take g = 10 m / sec^2 )

Sol. Given m = 100 kg s = 5 m

We know that

W = F * s ….(1)

We also know that

F = m g

Put this value in Equation (1)

W = m g s

W = 100 * 10 * 5

W = 5000 J

5. A car of mass 2000 kg is moving with uniform velocity 10 m/sec. Find the Kinetic energy of car ?

Sol. Given m = 2000 kg v = 10 m/sec

We know that

K = ½ * m * v^2

K = ½ * 2000 * 10^2

K = ½ * 2000 * 100

K = 1000 * 100

K = 10 * 10^4 J

6. A car of mass 1000 kg is moving with uniform velocity 5 m/sec. Find the Kinetic energy of car ?

Sol. Given m = 1000 kg v = 5 m/sec

We know that

K = ½ * m * v^2

K = ½ * 1000 * 5^2

K = ½ * 1000 * 25

K = 500 * 25

K = 12500 J

7. What work to be done to increase the velocity from 18 km/h to 36 km/h if the mass of bicycle is 50 Kg ?

Sol. Given m = 50 kg u = 18 km/h = (18 * 5) / 18 = 5 m/sec

v = 36 km/h = (36 * 5) / 18 = 10 m/sec

Initial kinetic energy = ½ * m * u^2

= ½ * 50 * 5^2

= 25 * 25 = 625 J

Final kinetic energy = ½ * m * v^2

= ½ * 50 * 10^2

= 25 * 100 = 2500 J

Work done = Change in kinetic energy

Work done = Final kinetic energy - Initial kinetic energy

= 2500 – 625

= 1875 J

8. What work to be done to increase the velocity from 36 km/h to 72 km/h if the mass of bicycle is 100 Kg ?

Sol. Given m = 100 kg u = 36 km/h = (36 * 5) / 18 = 10 m/sec

v = 36 km/h = (72 * 5) / 18 = 20 m/sec

Initial kinetic energy = ½ * m * u^2

= ½ * 50 * 10^2

= 25 * 100 = 2500 J

Final kinetic energy = ½ * m * v^2

= ½ * 50 * 20^2

= 25 * 400 = 10000 J

Work done = Change in kinetic energy

Work done = Final kinetic energy - Initial kinetic energy

= 10000 - 2500

= 7500 J

9. Find the energy by an object of mass 50 Kg when it at a height of 10 m. (Take g = 10 m/sec^2)

Sol. Given m = 50 Kg h = 10 m g = 10 m/sec^2

We know that

Potential Energy = m g h

= 50 * 10 * 10

= 5000 J

10. Find the energy by an object of mass 25 Kg when it at a height of 5 m. (Take g = 10 m/sec^2)

Sol. Given m = 25 Kg h = 5 m g = 10 m/sec^2

We know that

Potential Energy = m g h

= 25 * 10 * 5

= 1250 J

science-ncert-solution

11. A object of mass 40 kg at a height. If the potential energy of object is 800 J. Find the height of object? (Take g = 10 m/sec^2 )

Sol. Given m = 40 kg E(p) = 800 J g = 10 m/sec^2

We know that

Potential Energy = m g h

E(p) = m g h

h = E(p) / ( m g )

h = 800 / ( 40 * 10 )

h = 800 / 400

h = 2 m

12. A object of mass 20 kg at a height. If the potential energy of object is 600 J. Find the height of object? (Take g = 10 m/sec^2 )

Sol. Given m = 20 kg E(p) = 600 J g = 10 m/sec^2

We know that

Potential Energy = m g h

E(p) = m g h

h = E(p) / ( m g )

h = 600 / ( 20 * 10 )

h = 600 / 200

h = 3 m

13. Two army men, each weight have 100 Kg, climbs on a rope for height 5 m. First army man takes 5 sec and second army man takes 10 sec. Find the power expended by army man ?

Sol. a). Power expended by first army man

Given Weight = 100 kg h = 5 m t = 5 sec

We know that

Weight = m g = 100 kg

Power = Work Done / Time

P = W / t

P = (m g h) / t

P = (100 * 5) / 5

P = 100 W

b). Power expended by second army man

Given Weight = 100 kg h = 5 m t = 10 sec

We know that

Weight = m g = 100 kg

Power = Work Done / Time

P = W / t

P = (m g h) / t

P = (100 * 5) / 10

P = 50 W

14. Two army men, each weight have 140 Kg, climbs on a rope for height 6 m. First army man takes 7 sec and second army man takes 14 sec. Find the power expended by army man ?

Sol. a). Power expended by first army man

Given Weight = 140 kg h = 6 m t = 7 sec

We know that

Weight = m g = 140 kg

Power = Work Done / Time

P = W / t

P = (m g h) / t

P = (140 * 6) / 7

P = 120 W

b). Power expended by second army man

Given Weight = 140 kg h = 6 m t = 14 sec

We know that

Weight = m g = 140 kg

Power = Work Done / Time

P = W / t

P = (m g h) / t

P = (140 * 6) / 14

P = 60 W

15. A army woman of mass 72 kg runs on staircase 36 steps in 10 sec. If the height of each staircase is 12 cm. Find her power? (Take g = 10 m/sec^2 )

Sol. Given Weight = 72 kg

We know that

Weight = m g = 72 kg

h = ( 36 * 12 ) / 100 = 432 / 100

h = 4.32 m

t = 10 sec

Power = Work Done / Time

P = W / t

P = (m g h) / t

P = (72 * 4.32) / 10

P = 31.10 W

16. A army woman of mass 70 kg runs on staircase 30 steps in 10 sec. If the height of each staircase is 10 cm. Find her power? (Take g = 10 m/sec^2 )

Sol. Given Weight = 70 kg

We know that

Weight = m g = 70 kg

h = ( 30 * 10 ) / 100

h = 3 m

t = 10 sec

Power = Work Done / Time

P = W / t

P = (m g h) / t

P = (70 * 3) / 10

P = 21 W

17. A bulb of 7 w is used for 7 hours per day. Find units consumed in a day ?

Sol. Given P = 7 W = 0.007 kW t = 7 hours

Energy = Power * Time taken

= 0.007 * 7

= 0.049 kW/h = 0.049 units

18. A fan of 100 w is used for 7 hours per day. Find units consumed in a week ?

Sol. Given P = 100 W = 0.10 kW t = 7 hours

Energy = Power * Time taken

= 0.10 * 7

= 0.70 kW/h = 0.70 units

Energy consumed in a week = 7 * Energy consumed in a day

= 7 * 0.70 = 4.9 unit

19. A television of 200 w is used for 8 hours per day. Find units consumed in a month ?

Sol. Given P = 200 W = 0.20 kW t = 8 hours

Energy = Power * Time taken

= 0.20 * 8

= 1.6 kW/h = 1.6 units

Energy consumed in a month = 30 * Energy consumed in a day

= 30 * 0.70 = 21 unit

20. A fan of 100 W and a bulb of 7 W is used for 8 hours per day. Find units consumed in a month ?

Sol. a). Given P = 100 W = 0.10 kW t = 8 hours

Energy consumed by fan = Power * Time taken

= 0.10 * 8

= 0.80 kW/h = 0.80 units

Energy consumed in a month by fan = 30 * Energy consumed in a day

= 30 * 0.80 = 24 unit

b). Given P = 7 W = 0.007 kW t = 8 hours

Energy consumed by bulb = Power * Time taken

= 0.007 * 8

= 0.056 kW/h = 0.056 units

Energy consumed in a month by fan = 30 * Energy consumed in a day

= 30 * 0.007 = 0.21 unit

Total Energy consumed by fan and bulb in month = Energy consumed by fan + Energy consumed by bulb

= 24 + 0.21 = 24.21 units

Milan Tomic

Hi. I’m Designer of Blog Magic. I’m CEO/Founder of ThemeXpose. I’m Creative Art Director, Web Designer, UI/UX Designer, Interaction Designer, Industrial Designer, Web Developer, Business Enthusiast, StartUp Enthusiast, Speaker, Writer and Photographer. Inspired to make things looks better.