Applications of Newton

In a cricket match a fielder moves his arms back while trying to catch a cricket ball because if he tries to stop the fast moving ball suddenly then the speed decreases to zero in a very short time. Therefore the retardation of the ball will be very large. As a result the fielder has to apply a larger force to stop the ball. Thus, if he tries to stop a fast moving cricket ball the fielder may get hurt as the ball exerts a great pressure on the hands but if he tries to stop it gradually by moving his arms back then the velocity decreases gradually in a longer interval of time and hence retardation decreases. Thus the force exerted by ball on the hand decreases and the fielder does not get hurt.

A Fielder Moving his Hands Backward WhileTrying to Catch a Ball

An athlete before jumping runs some distance because this forward momentum may help him to jump high.

1)

Calculate the momentum of a toy car of 150 g moving with a speed of 5 m/s.

Solution:

Mass of the toy car (m) = 150 g

Velocity (v) = 5 m/s

Momentum (p) = mv

Momentum = 0.75 kg m/s

2)

Calculate the change in momentum of a body weighing 10 kg when its velocity decreases from 20 m/s to 0.2 m/s.

Solution:

Mass of the body (m) = 10 kg

Initial velocity (u) = 20 m/s

Final velocity (v)= 0.2 m/s

Change in momentum = m (v-u)

= 10 (0.2 - 20)

= 10 (-19.8)

Change in momentum = -198 N s

3)

A body of mass 50 kg has a momentum of 225 kgm/s. Calculate the velocity of the body.

Solution:

Mass (m) = 50 kg

Momentum (p) = 225 kgm/s

Velocity (v) = ?

Velocity = 4.5 m/s