WORK, POWER AND ENERGY

Question 1

What is work

Answer 1

Work is said to be done when the force applied on the body makes the body move

Question 2

Factors affecting measurement of work

Answer 2

. The magnitude of force applied
. Displacement produced by the force

Question 3

Measurement of work

Answer 3

W= F x S
The amount of work done is equal to the product of magnitude of force applied and the point of application of force in the direction of force

Question 4

When work is done how is it positive

Answer 4

If the displacement is in the direction of force
W = cos θ
θ=0
cos θ = 1
Work done is positive
Example : When a coolie raises a load upwards against gravity the work is said to be positive

Question 5

When work is done normal to the direction of force

Answer 5

When work is done normal to the direction of force then
W= F cos θ
θ = 90
cos 90= 0
Work done is zero
When a coolie is carrying a load and walking, no work is done against the force of gravity

Question 6

Conditions for the work done to be zero

Answer 6

. There is no displacement done
. The displacement is normal to the direction of force

Question 7

When work is done against the direction of force applied

Answer 7

When the displacement is against the direction in which the force is applied
W = F cos θ
θ = 180
cos θ= -1
w= -1
Example: when a ball is thrown vertically upwards from let’s say point A to point B, it goes upwards in the direction of force w= mgh but while going back downwards from point B to point A it is doing work against gravity hence w= -mgh

Question 8

How is work done 1 joule

Answer 8

1 Joule of work is said to be done when a force of 1 newton displaces the body through a distance of 1 m in its own directiom

Question 9

How is 1 erg of work done

Answer 9

1 erg of work is said to be done when a force of 1 dyne displaces the body through 1 cm in its own direction

Question 10

What is the relationship between erg and joule

Answer 10

1 J = 1 Nm
1 J = 10^5 dyne x 10^2cm
= 10^7 erg

Question 11

What is power how is it measured

Answer 11

The rate of doing work is called power
P= W/t

Question 12

Factors affecting power

Answer 12

. The amount of work done
. The time taken by the source to do work

Question 13

Speed and power relationship

Answer 13

P = F X V

Question 14

What is the unit of power and define it

Answer 14

SI unit = Watt
If one joule of work is done in one second then the power spent is said to be one watt

Question 15

Relationship between watt and erg

Answer 15

1 watt = 10^7 erg/s

Question 16

Difference between power and work

Answer 16

WORK:
. Work is said to be done when a force applied makes the body move
. Work done does not depend upon time taken

POWER:
. Power is the rate of doing work.
. Power depends upon amount of time spent

Question 17

What is energy

Answer 17

Energy is the capacity of a body to do work

Question 18

Unit of energy

Answer 18

1 J

Question 19

What is one watt hour what is its relationship with kJ

Answer 19

One watt-hour is the energy spent by a source of the power of one watt in one hour
1Wh= 3.6kJ

Question 20

Difference between Power and Energy

Answer 20

POWER:
. Power is the rate of doing work
. Power depends upon time taken

ENERGY:
. Energy is the capacity of a body to do work
. Energy does not depend upon time

Question 21

What is potential energy

Answer 21

The energy possessed by a body at rest due to its size, shape and position is called potential energy