Posted by **Joe** on Wednesday, January 13, 2010 at 3:58pm.

I'm having some trouble with this question

A 4200-kg rocket is traveling in outer space with a velocity of 120m/s toward the Sun. It needs to alter its course by 23 degrees, which can be done by shooting is rockets briefly in a direction perpendicular to it’s original motion. If the rocket gases are expelled at a speed of 2200 m/s relative to the rocket, what mass of gas must be expelled

I see that I need to find the other velocity

Vy = 120 tan 23

this gave me about 50.94 m/s

I do not know were to go from here

- Physics -
**Marth**, Wednesday, January 13, 2010 at 6:36pm
Let the rocket be traveling in the x direction, and the boosters fire in the y direction.

Actually you need to alter the velocity so that the 120m/s is the x component, and a y component exists making the angle 23 degrees.

tan(theta) = y/x

tan(23) = y/120

Now you can use that to find the required change in momentum. By conservation of momentum, the momentum of the expelled gases equals the change in momentum of the rocket. Use that to find the mass of the expelled gas.

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