Q. 44.4( 44 Votes )

# A motorcar of mass 1200 kg is moving along a straight line with a uniform velocity of 90 km/h. Its velocity is slowed down to 18 km/h in 4 s by an unbalanced external force. Calculate the acceleration and change in momentum. Also calculate the magnitude of the force required.

Answer :

Given,

Initial velocity, u = 90 km/h

=

= 25 m/s

Final velocity, v = 18 km/h

=

= 5 m/s

Acceleration, a =?

Time, t = 4 s

Now, v = u + at

5 = 25 + a × 4

4a = 5 – 25

4a = - 20

a = -

a = - 5 m/s^{2}

Therefore, the acceleration of the motorcar is -5 m/s^{2}.

Now we will calculate change in momentum:

Change in momentum = mv – mu

= 1200 × 5 - 1200 × 25

= 6000 – 30000

= - 24000 kg m/s

Therefore, change in momentum is 24000 kg m/s

Now we will calculate the magnitude of force:

Force, F = m × a

= 1200 × (-5)

= - 6000 N

Rate this question :

How long will it take a force of 10 N to stop a mass of 2.5 kg which is moving at 20 m/s?

Lakhmir Singh & Manjit Kaur - PhysicsThe physical quantity which makes it easier to accelerate a small car than a large is measures in the unit of:

A. m/s B. kg

C. kg m/s D. kg m/s^{2}

Explain why, a cricket player moves his hands backwards while catching a fast cricket ball.

Lakhmir Singh & Manjit Kaur - Physics