# Important Questions (1 mark): Work & Energy

## 25 Questions MCQ Test Physics for Class 9 | Important Questions (1 mark): Work & Energy

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Attempt Important Questions (1 mark): Work & Energy | 25 questions in 25 minutes | Mock test for Class 9 preparation | Free important questions MCQ to study Physics for Class 9 for Class 9 Exam | Download free PDF with solutions
QUESTION: 1

Solution:
QUESTION: 2

### In SI system, the unit of P.E. is

Solution: Joule. As potential energy is a form of energy so it's SI unit is also Joule. The gravitational potential energy has the same units as kinetic energy, kg m2 / s2. In fact, all energy has the same units, kg m2 / s2, and is measured using the SI unit is Joule (J).
QUESTION: 3

### Kilowatt hour (kWh) represents the unit of

Solution:

The kilowatt-hour (SI symbol: kW⋅h or kW h; commonly written as kWh) is a unit of energy equal to 3600 kilojoules (3.6 megajoules). The kilowatt-hour is commonly used as a billing unit for energy delivered to consumers by electric utilities.

QUESTION: 4

When speed of a motor car increases six times, then kinetic energy increases by

Solution:

Let initial speed of the car be v m/s and mass be m kg
Using the equation
K.E.= (mv²) / 2
It can be observed that, if we increase the speed (v) by 6 times the kinetic energy will increase by 36 times.

QUESTION: 5

1 kWh equals

Solution:
QUESTION: 6

When speed of the moving object is doubled its

Solution:
QUESTION: 7

When time taken to complete a given amount of work increases, then

Solution:
QUESTION: 8

When the force applied and the displacement of the body are inclined at 90° with each other, then work done is

Solution:
QUESTION: 9

The KE. of a body in increased most by doubling its

Solution:
QUESTION: 10

If a force F is applied on a body and it move with velocity v, then power will be :-

Solution:
QUESTION: 11

Work done by a centripetal force

Solution:
QUESTION: 12

Potential energy and kinetic energy are types of

Solution:

Mechanical energy is the energy that is possessed by an object due to its motion or due to its position. Mechanical energy can be either kinetic energy (energy of motion) or potential energy (stored energy of position).

QUESTION: 13

Work done in moving a 50 kg block through a horizontal distance of 10 m by applying a force of 100N which makes an angle of 60° with the horizontal is

Solution:

We know, work done :-
W = FS cos theta
Here, F = 100 ,  S = 10  , theta = 60°
So,   W =  100 * 10 * cos 60°
W   =  500 J

QUESTION: 14

kWh is the unit of

Solution:
QUESTION: 15

An elevator is designed to lift a load of 1000 kg through 6 floors of a building averaging 3·5 m per floor in 6 sec. Power of the elevator, neglecting other losses, will be

Solution:

Total height, h = 6 x 3.5 = 21 m
So total work done, W = mgh = 1000 x 9.8 x 21 = 205800J
Power, P = W/t = 205800 / 6 = 3.43 x 104 watt

QUESTION: 16

The work done by a body is directly proportional to :

Solution:
QUESTION: 17

Work done is said to be positive when a force causes displacement:

Solution:
QUESTION: 18

The work done on an object does not depends on the

Solution:
QUESTION: 19

In which case work is not done:

Solution:
QUESTION: 20

In which case work is done:

Solution:
QUESTION: 21

A stone is tied to a string and whirled in a circular path. The work done by the stone is :

Solution:
QUESTION: 22

In order to do work, energy is

Solution:
QUESTION: 23

A rocket rises up in the air due to the force generated by the fuel. The work done by the:

Solution:

As the rocket moves in the direction of force generated by fuel, therefore it is positive work. As the force of gravity acts in the direction opposite to the displacement. Therefore, it is negative work.

QUESTION: 24

One joule work is said to be done when a force of one newton acts through a distance of:

Solution:
QUESTION: 25

Work is the product of time and:

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