Question

A person on a bridge 25m above the water throws a rock straight downwards at 20m/s.

a. How long does it take to hit the water?
B how fast is it going when it hits?

Answer 1

a) Δd=v₂Δt+
`\frac {1}{2}`aΔt²

v₂=0 (hits ground)

Δd=
`\frac {1}{2}`aΔt²

Δt²=Δd÷
`\frac {1}{2}`a

t=√25÷
`\frac {1}{2}`(9.8) 9.8m/s²=gravity

t=5÷4.8

t=1.04s

b) a=
`(v_2-v_(1) )/(t)`

a×t=v₂-v₁

v₂=(a×t)+v₁

v₂=(9.8×1.04)+20

v₂=10.192 + 20

v₂=30.192

v₂=30.2m/s rounded