CBSE Class 9 Answered
On a level road, a scooterist applies brakes to slow down from a speed of 10m/s to 5 m/s. If the mass of the scooterist and the scooter be 150 kg, calculate the work done by the brakes. (Neglect air resistance and friction).
Asked by rajneesh kumar | 29 Nov, 2013, 01:30: PM
Expert Answer
Method 1
As per work-kinetic energy theorem , change in kinetic energy resulting from application of external forces is equal to work done.
Here m1 = m2 = m = mass of the scooterist + mass of scooter = 150 kg
W= Ek1 - Ek2
= 
= 1/2 x 150 x (10)2 - 1/2 x 150 x (5)2
= 5625J
Method 2
u = 10 m/s
v = 5 m/s
total mass = 150 kg
third eq. of motion :- v2 - u2 = 2as
s = (v2 - u2) / 2a ...... (1)
W = Fs .......(2)
F = ma .........(3)
from (1),(2),(3)
W = ma x (v2 - u2) / 2a
From this method also you will get same answer.
Answered by Komal Parmar | 29 Nov, 2013, 02:38: PM
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