Question

1. A ball is thrown dowuward from the top of a 40 m high building at a velocity of 5.0 m/s.
a) Find the time it takes to reach the ground.
b) Find the average velocity of the ball during its motions
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Answer 1

Answer:

4s

u=+10m/s, a=−10m/s

2

ands=−40m

(at the point where stone strikes the ground)

Substituting in s=ut+

2

1

at

2

, we have

−40=10t−5t

2

or 5t

2

−10t−40=0

or t

2

−2t−8=0

Solving this, we have t=4s and −2s. Taking the positive value t=4s.