Question

Question 4 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.

Class 9 - Science - Force and Laws of Motion Page 130

Answer 1

Given info : 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.

To find : the acceleration and change in linear momentum and also magnitude of force required.

solution : initial velocity, u = 90 km/h

= 90 × 5/18

= 25 m/s

final velocity, v = 18 km/h

= 18 × 5/18

= 5 m/s

we know, acceleration = change in velocity with respect to time.

so, acceleration, a = (final velocity - initial velocity)/time taken

= (5 - 25)/4

= -20/4

= -5 m/s²

change in linear momentum = final linear momentum - initial linear momentum

= mv - mu

= m(v - u)

= 1200 kg × (5 m/s - 25 m/s)

= 1200 kg × -20 m/s

= -24000 kgm/s

magnitude of force required, F = ma

= 1200 kg × 5 m/s² [ just taking magnitude of acceleration because we have to find magnitude of force ]

= 6000 N

Answer 2

HELLO FRIEND HERE IS YOUR ANSWER,,,,,,,,

Refer and consult the following attachments for a detailed explanation and step by step solution along with time by time elaborations to reach the final conclusion in our answers....

[Check attachments for explanation]

$\boxed{\bf{Acceleration \: of \: this \: vehicle = a = - 5 \: m/s^2}}$

$\boxed{\bf{Change \: in \: momentum \: of \: this \: vehicle = M_{(v - u)} = - 24000 \: Kg \: m/s}}$

Magnitude of the force required to slow down the vehicle by an unbalanced external force;

$\boxed{\bf{F = - 6000 \: N}}$

HOPE THIS HELPS YOU AND CLEARS THE DOUBTS!!!!