Question

A ball is thrown vertically upwards with a velocity of 20m/s from the top of a multistory building. The height of the point from where the ball is thrown is 25m from the ground. How high will the ball rise? (Take g=10(SI units))
can anybody tell the reference book for this question

Answer 1

Explanation:

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Correct option is

A

t=5s

Time to reach maximum height can be obtained from v=u+at

0=20+(−10)t

t=2s

s=ut+0.5at

2

=20(2)+0.5(−10)(2)

2

=20m

Thus, total distance for maximum height is 45 m

s=ut+0.5at

2

45=0+0.5(10)(t

′

)

2

t

′

=3s

Total time= 3+2= 5s

Answer 2

Explanation:

Time to reach maximum height can be obtained from v = u + at

0 = 20 + (−10)t

t = 2s

s = ut + 0.5at^2 =20(2)^2 + 0.5(−10)(2)

=20m

Thus, total distance for maximum height is 45 m

s = ut + 0.5at^2

45 + 0 + 0.5 ( 10 )( t`)^2

t` = 3s

total time = 3 + 2 = 5s