# Second Law of Motion

## •    Newton’s second law states that the rate of change of linear momentum of the body is directly proportional to the force applied on it and the change takes place in the direction of the applied force. Mathematically,                                                                              F = ma where, m is the mass and a is the acceleration of the body. Linear momentum (p) is defined as the product of the mas and velocity of a body. The SI unit of force is newton (N). A force is said to be one newton, if it is acting on a body of mass one kilogram produces an acceleration of one meter per second square in it. •    A few daily life applications of Newton’s second law of motion are, a cricket player moves his hands backwards while catching a fast moving ball, stretchable seat belts of vehicles and high jumpers are made to jump on a heap of sand.In all the given examples, momentum is reduced thereby reducing the effect of force.

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• Q1

Newton’s second law gives the measure of

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force

##### Explanation:

The second law of motion states that the rate of change of momentum of an object is directly proportional to the applied external unbalanced force in the direction of force. Hence, this law gives the measure of force.

• Q2

A body of mass 10 kg and velocity 10 m/s collides with a stationary body of mass 5 kg. After collision, both bodies stick to each other. The common velocity of the system would be

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20/3 ms-1 .

##### Explanation:

• Q3

A body of mass m collides against a wall with a velocity v and rebounds with the same velocity. The change in the momentum of the wall is

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zero

##### Explanation:

Final velocity(v) and initial velocity of the wall is same = 0

therefore;

Change in the momentum of the wall = 0 - 0 =0