Homework Help: More momentum

1. Apr 5, 2006

Drevin

A 5kg model vehicle travelling at 14 m/s experiences a rocket boost of 85N (in the direction of motion) for 20s. What is the resulting speed?

I tried using:

F = mv/t, but that didn't work out for me.

85 = 5v/20
85*20 = 5v
1700/5 = v
v = 340 m/s

but, that's wrong... what am I doing incorrectly? thanks.

edit: I guess you could consider impulse actually, heh... whoops

2. Apr 5, 2006

barob1n

Try

v(t)=v_initial + a*t

F=m*a ----> a=F/m

Last edited: Apr 5, 2006
3. Apr 6, 2006

daniel_i_l

In this case F*t = mVf - mVi, in other words, the Ft equals the change in momentum.