I have a question I need help with (acceleration)

1. Jun 25, 2004

tee1

I have a question I need help with

I am having trouble figuring out what to do with this problem. Can anyone help?

An automobile starts from rest and accelerates to a final velocity in two stages along a straight road.Each stage occupies the same time. In stage 1, the magnitude of the car's acceleration is 3.0 m/s^2. The magnitude of the car's velocity at the end of stage 2 is 2.5 times greater than it is at the end of stage 1. Find the magnitude of the acceleration in stage 2.

2. Jun 25, 2004

Goalie_Ca

2.5*(3t) = 3t + a * (t)
7.5t - 3t = at
4.5t = at
a = 4.5

wow, i hope i didn't make any mistakes.

edit: i did lol, too late for me. such sillyness. (rechecks my stats homework)

Last edited: Jun 25, 2004
3. Jun 25, 2004

KnowledgeIsPower

Stage one:
V = ?, u = 0, a = 3ms^-2, t=t
v=u+at
?=3t

Velocity at end = 2.5(3t) = 7.5T

Stage two:
U = 3t, V = 7.5t, a = ?, t=t
v = u + at
7.5t = 3t + at
divide through by t
7.5=3+a
a=7.5-3
a=4.5ms^-2

Where U = speed at the beggining of the stage, V = Final speed, T = time, a = acceleration.
Kinematics is fun, don't be afraid to leave things as unknowns in algebraic form if you have to compile information in two stages. A lot of examination 'proof' questions will ask for this.

Last edited: Jun 25, 2004