Question

is the
A4. 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.
please tell me
​

Answer 1

GIVEN :

• Mass, m = 1200 kg
• Initial velocity, u = 90 km/h = 25 m/s
• Final velocity, v = 18 km/h = 5 m/s
• Time taken, t = 4 s

FORMULA :

1. Change in momentum, m$\sf \: = \: \dfrac {(Final velocity \: - \: initial velocity)}{time \: taken}$

2. Force = $\sf \dfrac {Change \: in \: momentum}{time}$

TO FIND :

Acceleration.

change in momentum.

Magnitude of the force required.

SOLUTION :

According to the first law of motion,

V = u + at.

5 = 25 + a(4)

a = $\sf a \: = \: 5m/s^{2}$

★ Change in momentum, $m \: = \: \dfrac {(Final velocity \: - \: initial velocity)}{time \: taken}$

→ $\sf 1200 \: \times \: (25 - 5)$

→ $\sf = 24000 \: kg \: m/s$

★ Force = $\sf \dfrac {Change \: in \: momentum}{time}$

→ $\sf \dfrac {24000}{4}$

→ $\sf = 6000 \: N$