A child attempts to roll a ball up a long ramp and it slows as it goes up. If it is released at 2.5 m/s upward and accelerates downward at 0.8 m/s2, how fast is the ball moving after 4 seconds?

-0.7 m/s

Explanation:

Initial velocity (u)= 2.5 m/s

Acceleleration (a)= -0.8 m/s^2

Time taken (t) = 4  seconds

Hence,

v=u+at [1st Equation of motion]

v=2.5+-0.8*4

v=2.5-3.2

v=-0.7 m/s

Note that the negative sign indicates that the ball has changed direction and rolls downwards with gravity