CBSE Class 9 Science Chapter 11: Work and Energy NCERT Solutions

Work is done when a force causes an object to move. The amount of work done is calculated by multiplying the magnitude of the force by the distance the object moves in the direction of the force.

The formula for work done (W) is given by:

$$W\; =\; F\; \backslash times\; S$$

Where:

• $F$ is the magnitude of the force applied.
• $S$ is the distance of displacement in the direction of the force.

Given in the problem:

• Force, $F\; =\; 7\; \backslash text\{\; N\}$
• Displacement, $S\; =\; 8\; \backslash text\{\; m\}$

Substituting these values into the formula:

$W\; =\; 7\; \backslash text\{\; N\}\; \backslash times\; 8\; \backslash text\{\; m\}$

$W\; =\; 56\; \backslash text\{\; Nm\}$

Since 1 Newton-meter (Nm) is equal to 1 Joule (J), the work done is:

$W\; =\; 56\; \backslash text\{\; J\}$

Therefore, the work done in this case is 56 Joules.

In physics, work is considered to be done on an object when two conditions are met:

1. A force must be applied to the object.
2. The object must be displaced (move from its position) as a result of the applied force, and this displacement must have a component in the direction of the force.

If either of these conditions is not met (e.g., a force is applied but there is no movement, or the object moves but no force is applied), then no work is done in the scientific sense.

When a force acts on an object and causes it to move through a certain distance in the same direction as the force, the work done is calculated by multiplying the magnitude of the force by the distance of displacement.

The expression for work done (W) is:

$$W\; =\; F\; \backslash times\; s$$

Where:

• $W$ represents the work done.
• $F$ represents the magnitude of the force applied.
• $s$ represents the distance of displacement in the direction of the force.

One Joule (1 J) is defined as the amount of work done when a force of one Newton (1 N) causes an object to be displaced by one meter (1 m) in the direction of the applied force.

Mathematically, this can be represented as:

$$1\; \backslash text\{\; J\}\; =\; 1\; \backslash text\{\; N\}\; \backslash times\; 1\; \backslash text\{\; m\}$$

This means if you apply a force of 1 Newton and it moves an object exactly 1 meter in the direction you are pushing or pulling, you have done 1 Joule of work.