A 1 000-kg experimental rocket sled at rest on level frictionless rails is loaded with 50 kg of propellant.It exhausts the propellant in a 20-s "burn." The rocket moves at 150 m/s after the burn.What average force is experienced by the rocket during the burn? A)0.95 x 10⁴ N B)0.75 x 10⁴ N C)0.60 x 10⁴N D)0.35 x 10⁴ N

Question

Quizplus · Accepted Answer

First, we can use conservation of momentum to find the initial velocity of the propellant and the sled combined:

(1000 kg + 50 kg) * 0 m/s = 1000 kg * v_initial

v_initial = 0 m/s

After the burn, the final momentum of the system is:

(1000 kg + 50 kg) * 150 m/s = 157500 kg*m/s

Using conservation of momentum again, we can find the change in momentum of the system during the burn:

Δp = 157500 kg*m/s

The average force during the burn is equal to the change in momentum divided by the duration of the burn:

F_avg = Δp / t = (157500 kg*m/s) / 20 s

F_avg = 7875 N

This is equivalent to 0.75 x 10^4 N, which matches choice B.

A 1 000-Kg Experimental Rocket Sled at Rest on Level