Physics question A spacecraft descends vertically near the surface of Planet X. An upward thrust of 25.0kN from its engines slows it down at a rate of 1.20 m/s^2, but if an upward thrust of only 10.0 kN is applied, it speeds up at rate of .80m/s^2.

Question

Physics question A spacecraft descends vertically near the surface of Planet X.  An upward thrust of 25.0kN from its engines slows it down at a rate of 1.20 m/s^2, but if an upward thrust of only 10.0 kN is applied, it speeds up at rate of .80m/s^2.

precal · Answer

What is the direction of the acceleration of the spacecraft in the case of 25.0kn thrust?

precal · Answer

I need to draw a free body diagram for the spacecraft in the case of 25.0 kN thrust, any help is greatly appreciated.

zzr0ck3r · Answer

up. It is being slowed down.

precal · Answer

I know I need to draw force vectors with their tails at the dot. I have to pay attention to the relative length of one to the other.

zzr0ck3r · Answer

1 down 2 up.

zzr0ck3r · Answer

the second up one, is bigger.

precal · Answer

How about the direction of the acceleration of the spacecraft if I change the case to be 10.0 kN thrust?

zzr0ck3r · Answer

err first one up is bigger

zzr0ck3r · Answer

o yeah, sorry I got the two backwards.

zzr0ck3r · Answer

original : down.
first thrust: up
second thrust: down

precal · Answer

|dw:1348004842848:dw|like this boy I am having problems drawing these because I was taught that force is a parallelogram by my calculus teacher

zzr0ck3r · Answer

its only up and down.

zzr0ck3r · Answer

no diagonals.

zzr0ck3r · Answer

so we have what ever caused it to go down(prob gravity). this is pointing down.

then we add some force pushing up ( the thrust...just imagine a hand pushing it up). This slows it down, so it is not stronger than gravity because the ship is always descending. 

we then lessen the thrust, so it starts to move faster down, but is still (assumed I think) to be going down and not going faster than we were originally going.

precal · Answer

how about the directionof the acceleration of the spacecraft in the case of 10.0 kN thrust? is it still up?

zzr0ck3r · Answer

because the only reason you would use thrust in this situation, seemingly, would be to slow it down.

precal · Answer

Do you know Newton's second law?  I have to apply it to each case to find the spacecraft's weight near the surface of Planet X.

zzr0ck3r · Answer

no, down. 

Imagine the first thrust going up. Imagine your hand pushing up against the ship enough to slow it down but not make it go the opposite direction. Now imagine you stop pushing as hard, so it speeds up its descent.

when it speeds up, the acceleration is positive, when it slows down the acceleration is negative. (if we take positive to be down, and negative to be up)

precal · Answer

Newton's second law|dw:1348005364198:dw| I hope this is it