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## Homework Statement

Lets imagine we are back in 1969 and the Apollo Lunarlander is on approach to the moon. It has a mass of 200 kg and initial velocity of v1 = 6 m/s. The Astrofolks push the big red button in the cabin and engine burst of energy to break the spacecraft where time = 2 sec the resulting Force of the engine is 800 Newton and time = 4 sec the Force produced of the engine is 800 Newton. Whats the velocity of the decending lunar lander at t = 5 sec?

My professor did a fancy calculation where he included the mass of spacecraft and the resulting force of the engine bursts. But I tried something else :)

Lets imagine that after the they used the engine to break the spacecraft that its free-falling towards to the moon then.

## The Attempt at a Solution

[tex]v_{final} = v_{initial} - g_{moon}\cdot t[/tex] where t = 5 sec and [tex]g_{moon} = 1.62 m/s^2[/tex]

Then I plug this into the formula I get:

[tex]v_{final} = 6 m/s - 1.62 \cdot 5 = - 2.1 m/s[/tex]

Since the engine isn't given bursts at t = 5 then can't the LL be see as free falling and we can disregard its mass? And since the LL is decending the the final velocity is negativ?

Sincerely

Susanne