# physics homework

• July 4th 2007, 09:20 AM
twistedmexican
physics homework
An experimental rocket car starting from rest reaches a speed of 560 km/h after a straight 400-m run on a level salt flat. Assuming that acceleration is constant, (a) what was the time of the run, and (b) what is the magnitude of the acceleration?:confused:
• July 4th 2007, 11:44 AM
janvdl
Quote:

Originally Posted by twistedmexican
An experimental rocket car starting from rest reaches a speed of 560 km/h after a straight 400-m run on a level salt flat. Assuming that acceleration is constant, (a) what was the time of the run, and (b) what is the magnitude of the acceleration?:confused:

Let's do b) first.

$v^2 = u^2 + 2as$

$v = 155,5 m s^{-1}$

$24197,5 = 0 + 2a(400)$

$a = 30 m s^{-1}$

Now a)

$v = u + at$
$155,5 = 0 + (30)t$
$t = 5,18$