Velocity - time home work check

[jacknjersey]

Homework Statement

A car accelerates from 0 to 30m s ^-1 in 5.0 seconds, travels at a constant 30m s^-1 for 15.0 seconds and then brakes to a stop in 10.0 seconds.

1) calcualte the acceleration (assumed constant) in each section of the motion.
2) calculate distance travelled
3) what is 30m s^-1 in km/h?

Homework Equations

a= change in velocity / change in time
d(t) = v_0 x t + (a/2)t^2

The Attempt at a Solution

a=(30-0)/5 = 6 m/s
d(t) = 0 x 5 +(6/2_ x 5^2 = 75m

a=(30-30)/15 = 0 m/s^2
d(t) = 30 x 15 + (0/2) x 15^2 = 450m

a=(0-30)/10 = -3m/s^2
d(t) = 30 x 10 + (-3/2) x 10^2 = 150m

 

[PhanthomJay]

Looks OK!

 

[jacknjersey]

Thanks so much! I'm working so slowly trying to get it right. Thanks again, the feedback is a boost!