An unfueled 1000-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 160 m/s after the burn.What average force is experienced by the rocket during the burn? A)0.80 × 10⁴ N B)0.75 × 10⁴ N C)0.60 × 10⁴ N D)0.35 × 10⁴ N

Question

Quizplus · Accepted Answer

The average force experienced by the rocket during the burn is equal to the change in momentum of the rocket divided by the time of the burn. The change in momentum is equal to the final momentum minus the initial momentum. The final momentum is equal to the mass of the rocket times its final velocity. The initial momentum is equal to zero because the rocket is at rest initially. The time of the burn is 20 s. Therefore, the average force experienced by the rocket during the burn is:$$F = \frac{mv_f - 0}{t} = \frac{(1000 kg)(160 m/s)}{20 s} = 8000 N$$

An Unfueled 1000-Kg Experimental Rocket Sled at Rest on Level