A rocket is moving through space at 120m/s. When its retro rockets are fired, it experiences an acceleration of -8m/s^2. If the retro rockets are fired for 20 seconds, determine the final velocity of the rocket.

Question

egenriether · Answer

use the fact that the acceleration multiplied by the time of acceleration is a velocity.  Then use the fact that velocities add.  So it looks like the negative acceleration will cause a decrease in the initial velocity.  Calculate how much then add them up (one will be negative)

richyw · Answer

well you are given an initial velocity $v_0=120m/s$ and a constant acceleration $a=-8m/s^2$. Both of these are vectors, but here we are assuming that the acceleration is in the same direction as the initial velocity (you can think about both of them being along the x axis. 

You are told that the rockets are fired for 20 seconds this gives us $\Delta t=20s$

Now for because this is a constant acceleration you can solve for the final veolocity $$v=v_0+a\Delta t$$

anonymous · Answer

So the final velocity for the rocket will be -40m/s?

anonymous · Answer

Thank you so much by the way man, it really helps

richyw · Answer

yup, and no worries!

anonymous · Answer

Awsome, and it works in the other formula solving for v2: d=(v1+v2)/2(t)
After finding a displacement of 800, i plugged it all in and solved out the equation 800=(120+v2)/2(20).

anonymous · Answer

Your way is much easier