An object of mass 5kg falls from rest and hits the ground at a speed of 20m/s. Air resistance is
negligible.
From what height has the object fallen?

Answer:

19) B

From rest indicates the initial velocity (u) = 0

Final velocity (v) = 20 m/s

Mass = 5 kg

Acceleration (g) = 10 m/s²

Using SUVAT equation,

v = u + at

t = (v – u) ÷ a

t = (20 – 0) ÷ 10 = 20 ÷ 10

t = 2 seconds

s = ut + ½at²

s = 0 + ½ x 10 x 2²

s = 5 x 4 = 20 m