Time to Accelerate from 30.0 m/s to 50.0 m/s - 5s

[soulja101]

Homework Statement

How long will it take a mass to accelerate from 30.0m/s (south) to 50.0m/s(north) if its acceleration isa sonstant 4.0m/s2(north)

Homework Equations

displacement=V/Time
Aav=V/time

The Attempt at a Solution

a=4.0ms2
v=20ms
d=Vav*time
time=v/acceleration
20ms/4.0ms2
=time is 5s

 

[cristo]

No, you have the correct equation, but your change in velocity is incorrect. At the beginning, the mass is moving 30 m/s south and we want it to accelerate and reach 50m/s north. Remember that velocity is a vector.

 

[danield]

i think u can use this simple formula whcih is
time= change in velocity (vf-vi)/ acceleration
and remember south and north are oppostite directions *hint*