A 95 kg falling trunk strikes the ground with a speed of 40 m/s. Assuming that there is no loss of energy due to air resistance, what is the height from which the trunk falls?

80 m or 81.3 m

Explanation:

Initially it had no velocity(as at rest). Let the height be h

Using conservation of energy:

Initial KE + PE = final KE + PE

(1/2) m(0)² + mgh = (1/2) m(40)² + mg(0)

mgh = (1/2) m (1600)

2gh = 16000

h = 1600/(2*10) {for g = 10}

h = 80

80 For g = 9.8, h = 81.3 m

Using Newton's eqⁿ of motion:

v² = u² + 2aS

40² = 0² + 2(g)S

1600/2g = S

For g = 10, S = 80 m

g = 9.8, S = 81.33 m

v=ir = 3x15 =45 v