HARD
9th CBSE
IMPORTANT
Earn 100

A body is allowed to fall under the influence of gravity from a height h. When does its

(i) potential energy become maximum;

(ii) potential energy equal kinetic energy;

(iii) kinetic energy become maximum?

Important Questions on Work and Energy

MEDIUM
9th CBSE
IMPORTANT
Secondary Physics>Chapter 5 - Work and Energy>EXERCISES>Q 5
An object of mass 3 kg is thrown vertically upward with a velocity of 10 m/s. Find
(i) the kinetic energy of the body at the time of throwing,
(ii) its potential energy of the body at the highest point.
HARD
9th CBSE
IMPORTANT
Secondary Physics>Chapter 5 - Work and Energy>EXERCISES>Q 6
A 500 W electric bulb lighted for 2 hours everyday and an electric motor of 0.5 horse power is used for 2 hours everyday. Calculate the cost of using the bulb and the motor for 30 days, if the cost of electrical energy is three rupees per unit.
MEDIUM
9th CBSE
IMPORTANT
Secondary Physics>Chapter 5 - Work and Energy>EXERCISES>Q 7
What is meant by power? Define the terms watt and kilowatt. Also state the bigger units of power.
MEDIUM
9th CBSE
IMPORTANT
Secondary Physics>Chapter 5 - Work and Energy>EXERCISES>Q 8
Derive the relationship between momentum and kinetic energy of a body.
MEDIUM
9th CBSE
IMPORTANT
Secondary Physics>Chapter 5 - Work and Energy>EXERCISES>Q 9

Differentiate between work, power and energy.

MEDIUM
9th CBSE
IMPORTANT
Secondary Physics>Chapter 5 - Work and Energy>EXERCISES>Q 10
An electric heater of 1000 W is used everyday for 70 minutes. Calculate the units of electrical energy this heater will consume in 30 days of use.
MEDIUM
9th CBSE
IMPORTANT
Secondary Physics>Chapter 5 - Work and Energy>EXERCISES>Q 11
A bag of wheat weighing 8 kg is lifted through a height of 12 m in 5 seconds with a constant velocity. Calculate the power developed during the process.
MEDIUM
9th CBSE
IMPORTANT
Secondary Physics>Chapter 5 - Work and Energy>EXERCISES>Q 12

A force of 200 N acting at an angle of 45° to the horizontal does a work of 45000 J. Calculate the displacement caused by the force in horizontal direction. (Take cos 45°=0 .7071)