A ball is projected horizontally. After 3 second from projection its velocity becomes 1.25 times of the velocity of projection. Its velocity of projection is:-

a) 10 m/s

b) 20 m/s

c) 30 m/s

d) 40 m/s

Answer: d) 40 m/s

Solution:

vy = uy + ayt

vy = 0 + 9.8 x 3

= 29. 4 m/s

v’ = √vx2 + vy2

= √vx2 + (29.4)2

(1.25 vx)2 = vx2 + (29.4)2

1.562vx= vx2 + (29.4)2

0.562vx= (29.4)2

vx = (29.4)2/0.562

vx ≈ 40 m/s

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