science
Grade-9
Easy

Question

A ball is dropped from the top of a building of height 80 m. Considering the acceleration due to gravity of the Earth to be 10 m/s2, the velocity of the ball right before it touches the ground is ____ m/s.

hintHint:

40 m/s

The correct answer is: 40


    Given that,
    The initial velocity, u = 0
    The acceleration, a = 10 m/s2
    The displacement, s = 80 m
    On using the third equation of motion we get,
    v2 = u2 + 2as
    Or, (v)2 = 0 + 2 x 10 x 80
    Or, (v)2 = 1600
    Or, v = √(1600)
    Or, v = 40 m/s
    Therefore, the velocity of the ball before hitting the ground is 40 m/s.

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