Question

. 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 seconds by an unbalanced force. Calculate the acceleration,

change in momentum. Also calculate the force applied.​

Answer 1

Given:

m = 1200 Kg

u = 90 $\frac{km}{h}$ = 25 $\frac{m}{s}$           (∵1$\frac{km}{h}$= $\frac{5}{18}$   $\frac{m}{s}$ )

v = 18 $\frac{km}{h}$ = 5 $\frac{m}{s}$

t = 4 seconds

To find:

1. acceleration
2. momentum
3. force applied

Solution:

1.

v = u + at

5 = 25 + a × 4                

a = −5  $\frac{m}{s}$   (-ve sign shows retardation)

2.

ΔP = mv − mu

ΔP = 1200 × 5 − 1200 × 25

ΔP = −24000  kg $\frac{m}{s}$

3.

∣F∣ = m ∣a∣

   = 1200 × 5

   = 6000 N