Vectors and Acceleration in a Straight Line

[Peter G.]

What is the change in velocity when:
a) 6.0 m/s becomes - 15 m/s
b) 5.0 m/s East becomes 15 m/s West

My doubt is mainly the notation: How I should answer, here is my try:

a) -9 m/s with 180 degrees change in direction
b) 9 m/s with from direction bearing 90 degrees to 270 degrees

And: A baby buggy rolls down a ramp which is 15 m long. It starts from rest and accelerates uniformly and takes 5.0 seconds to reach the bottom:
a) Average Velocity: 15 /5 = 3 m/s

Now, b asks for the velocity at the bottom. I don't know how to calculate the velocity without the acceleration, which is asked in question c)

c) s = ut x 1/2at^2
a = 1.2 m/s^2

and then

b) v = u + at
v = 6 m/s

Anyone can teach me how to get the velocity without the acceleration and with the notation in the first question?

Thanks,
Peter

 

[verty]

You can find the final velocity with this formula (only when acceleration is constant):

s = t(u+v)/2

 

[Peter G.]

Aw, yea that's right, thanks.

And what about my answers to the first question? Think they are O.K?