Physics question?

Question

A car with a velocity of 25m/s [E] changes it's velocity to 25m/s [S] in 15sec. Calculate the car's average acceleration.
um, i just want to know do i have to change one of 25m/s to minus sign?? and the answer for this question is 2.4m/s^2 [45 degerees S of W] thx :)

Answer 1

If it is traveling East and changes to South, then the acceleration in the East is
0=25+a*15
a=-25/15

and acceleration in the South is
25=a*15
a=25/15

since this is a vector, the magnitude is
sqrt(25^2/15^2 + 25^2/15^2)
or sqrt(2)*25/15
=2.4 m/s

The angle is ATAN(1), or 45 degrees South of East

j