Question

John Glenn's 1300 kg Mercury capsule orbited at 7800 m/s (Eastward) velocity, before retrorockets pushed westward: 4450 N for 5 s, 8900 N for 10 s, 4450 N for 5s.

b) what was the total Impulse from the retro-rockets?

b) what was the quickest acceleration caused by the retrorockets? (ignore gravity here)

Answer 1

b) The total impulse from the retro-rockets is the sum of the impulse from each individual engine firing. The impulse from each firing is the force applied multiplied by the duration of the firing. Therefore, the total impulse is (4450 N x 5 s) + (8900 N x 10 s) + (4450 N x 5 s) = 22,250 Ns + 89,000 Ns + 22,250 Ns = 133,500 Ns.

b) The quickest acceleration caused by the retrorockets is the change in velocity divided by the duration of the retrorocket firing. Since the retrorocket firing is done in three stages, we need to find the acceleration for each stage and then take the maximum value. The first stage acceleration is (4450 N)/(1300 kg)= 3.4 m/s^2, the second stage acceleration is (8900 N)/(1300 kg)= 6.8 m/s^2, the third stage acceleration is (4450 N)/(1300 kg)= 3.4 m/s^2. So the quickest acceleration is 6.8 m/s^2.