Question

$\huge\mathbb\red{QUESTION}$
A car of mass 2500 kg travelling at a speed of 40 m/s stops after covering a distance of 50 m when brakes are applied. Calculate (i) the force exerted on it by the brakes (ii) work done by brakes.
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Answer 1

Given, m = 2500kg ; u = 40m/s

S = 50m (after applying brakes)

(i) v² - u² = 2as

0 - (40)² = 2a(50)

a = -1600/100 = -16m/s²

F = ma = (2500)(-16)

= –40000N

Here force is nothing but friction.

Friction is opposite to motion.

So, F = 40000N = 4 × 10^4 N

(ii) W = FS

W = 40000 × 50

W = 2000000J

W = 2 × 10^6 J