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Selina Solutions Class 9 Physics Solutions for Exercise 3C in Chapter 3 - Chapter 3 Laws Of Motion

Question 31 Exercise 3C

A car of mass 480kg moving at a speed of 54km/h is stopped by applying brakes in 10s. Calculate the force applied by the brakes.

Answer:

Given: m=480kg, initial velocity, u=54km/h or 15m/s, final velocity, v=0m/s, t=10s, F=?

We know that acceleration is the rate of change of velocity

∴ acceleration = (v-u)/t

= (0-15)/10

= -1.5m/s2

The negative sign shows that it is retardation.

Force = m x a

= 480 (-1.5)

= 780N

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