Question

A car is moving in a straight line with speed
18 km h-!. It is stopped in 5 s by applying the brakes.
Find : (i) the speed of car in m s-1, (ii) the retardation
and (iii) the speed of car after 2 s of applying the
brakes. Ans. (i) 5 m s1, (ii) 1 m s2, (iii) 3 m s-​

Answer 1

(i) the speed of car in m/s= 5m/s

(ii) the retardation = -1m/s

(iii) speed of car after 2 seconds of applying the brakes = - 2.5m/s

Explanation:

Given Information -

• Initial velocity (u) =18km/hr
• Time taken to stop (t) =5 secs.
• Final velocity (v) =0km/hr

Mentioned Questions-

• (i) the speed of car in m/s.
• (ii) the retardation.
• (iii) speed of car after 2 seconds of applying the brakes.

Required Solution -

(i) the speed of car(Initial velocity) in m/s -

• $18 \times \frac{5}{18}$

• $=\sf\red{5m/s}$

ㅤ

(ii)the retardation-

Formula- ${\frac{v-u}{t}}$

• $= \frac{0 - 18}{5}$

• $= \frac{ - 5}{5}$

• $=\sf\green{ - 1m/s}$

ㅤ

(iii) speed of car after 2 seconds of applying brakes -

Taking time 2 seconds.

Formula- ${\frac{v-u}{t}}$

• $= \frac{0 - 5}{2}$

• $= \frac{ - 5}{2}$

• $=\sf\blue{ - 2.5m/s}$