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[tex]

v_f=v_i+a_s\Delta t

[/tex]

[tex]

s_f=s_i+v_i\Delta t+1/2a_s(\Delta t)^2[/tex]

[tex]

v_f^2=v_i^2+2a_s\Delta s

[/tex]

Ok first problem:

A Porsche challenges a Honda to a 400-m race. Because the Porsche's acceleration of 3.5m/s^2 is larger than the Honda's 3.0m/s^2, the Honda gets a 50-m head start. Both cars start accelerating at the same instant.

Who wins?

I used the 3rd equation to get 2800 and then sqrt 2800 to get Vf=53. Then I used the 1st equation to get delta t. Which I got to be about 15.14 sec. For the Honda I did the same thing and got 15.33 sec. So the Porsche wins. I was wondering. Did I do this right?

The second question...

A 1000kg weather rocket is launched straight up. The rocket motor provides a constant acceleration for 16s, then the motor stops. The rocket altitude 20s after launch is 5100m. You can ignore any effects of air resistance.

This one completely stumped me. Cause no matter which equation I use, I get at least 2 variables... and is the 1000kg even important?