Question

2
A ball is thrown vertically upwards with a velocity of 20 m s-' from the top of a building The
height of the point from where the ball is thrown is 25 m from the ground. How long will it
be before the ball hits the ground? Take g = 10 m s?​

Answer 1

Answer:

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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)+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

Answer:

Maximum height it obtained

=> v = u+ at

=> 0 =20 + (-10) t

=> 10t = 20

=> t = 2

s = ut + 1/2 a(t)2

s = 20(2) + 1/2 (-10) (2)2

s = 20m

total distance for maximum height

is 45 m

s = ut + 1/2 a(t')2

45 = 0 + 1/2 (10) (t')2

t' = 3

total time taken = 3s + 2s= 5 second