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A ball is suspended by a thread from the ceiling of a car. The brakes are applied and the speed of the car changes uniformly from 36kmh1 to zero in 5s . The angle by which the ball deviates from the vertical (g=10ms2) is:
(A) tan1(13)
(B) sin1(15)
(C) tan1(15)
(D) cot1(13)

Answer
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Hint We will first find out the acceleration of the car. Finally we will find out the angle it makes with the vertical.
Formulae Used: a=(vu)t
Where, a is the acceleration of the body, v is the final velocity, u is the initial velocity and t is the time taken by the body.

Complete Step By Step Solution
Here,
u= 36 kmh1=10ms1
v=0kmh1=0ms1
t=5s
Now,
acar=(010)5
Now,
a=2ms2
tanθ=ag=210=15
Thus, the answer turns out to be θ=tan1(15) which is (C).
But,
Also,
If we take
sinθ=210=15
θ=sin1(15)

Hence, (B) is also correct.

Note We got the value of sinθ , we took anet=a2+g2 an d value turns out to be 10ms2. Also, we took only the magnitude as it only plays the role to form the angle.
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