Question

Question #558fa

Answer 1

If the ball slows down, that means the acceleration vector is pointing opposite to the direction of velocity vector. Since velocity is negative acceleration must be positive.

Explanation:

To see that acceleration is positive, without loss of generality, we can take the final velocity to be zero.
`vec a = (\Deltavecv)/(\Deltat) = (vec v_f - vec v_i)/(\Deltat)`

`vec v_i = -v_i;` (negative initial velocity)
`vec v_f = 0;` (ball slows down to halt eventually)

`vec a = (0-(-v_i))/(\Deltat) = +v_i/(\Deltat)`