How Long Should a Rocket Fire to Adjust a Satellite's Speed?

[pokeefer]

Homework Statement

Small rockets are used to make small adjustments in the speed of satellites. One such rocket has a thrust of 35 N. If it is fired to change the velocity of a 72 000 kg spacecraft by 63 cm/s, how long should it be fired?

Homework Equations

Momentum = Mass x Velocity

The Attempt at a Solution

After reading the instructions, I'm still having difficulty on this particular problem.

There is a formala called pbefore = pafter

Where momentum in one object transfers to another when hit. But I just don't know where to begin.

Thanks.

 

[Doc Al]

Hint: Consider the impulse delivered by the force. (Look it up!)

 

[pokeefer]

Thanks but I don't know what that has to do with my problem. Can you post an explanation of the formula or the solution?

 

[Doc Al]

What's the definition of impulse and what does it have to do with momentum? Look it up!

 

[pokeefer]

How am I supposed to calculate impulse with the information given?

 

[Doc Al]

What's the definition of impulse?

 

[pokeefer]

Iv'e gotten this solution:F = (mass x velocity) / time
35N = 72,000 x 0.63 / t
35N = 45,360 kg m/s / t
35t = 45,360kg m/s
T = 1296 seconds

Is it right?

 

[Doc Al]

Iv'e gotten this solution:


F = (mass x velocity) / time
35N = 72,000 x 0.63 / t
35N = 45,360 kg m/s / t
35t = 45,360kg m/s
T = 1296 seconds

Is it right?

Yes, very good.

Impulse = FΔt

And impulse equals the change in momentum, Δ(mv).

So:
FΔt = Δ(mv) = mΔv
Δt = mΔv/F