mass, final velocity, velocity knocked backward

Question

Gimli throws his axe with a force of 90N and an acceleration of 1.4 m/s2 (the axe is magical and accelerates after being thrown). It has an initial velocity of 8 m/s. Two seconds later, it hits and sticks in a stationary 75 kg orc 20 meters away.

a. What is the mass of Gimli’s axe?

b. What is the final velocity of Gimli’s axe?

c. With what velocity is the orc knocked backward?

Answer 1

a) F = ma

90 = m * 1.4

m = 64.286 kg

b)

V = at +Vo

V = 1.4 * 2 + 8 = 10.8 m/s

c)

We have to use conservation of momentum!

Ma = Mass Axe

Va = Velocity of Axe upon Impact

Mo = Mass Orc

Vo = Velocity of Orc upon impact (Stationary)

MaVa + MoVo = (Ma+Mo)Vao'

Vo = 0

MaVa = (Ma+Mo)Vao'

Va = V = 10.8 m/s

Vao' =Ma/(Ma+Mo) * Va

Vao' = 64.286/(75+64.286) * 10.8 = 4.984 m/s

Vao' = 4.984 m/s