Homework Help: Find out the time and velocity

Nothing may be wrong. If you chose the positive direction downwards, then v will be negative. What equation did you use?

 

Try assuming that the ball was thrown from the 10m mark up to the 40m mark instead of from ground. You know the distance between (40-10), the time between, and the acceleration. All you need is the initial velocity. You should have an equation for that. Once you find the initial velocity (which, from what you just solved is actually the velocity at 10m), this velocity becomes the final velocity. You also have the distance and acceleration. You need to then find the initial velocity (this time refering to the ground). Good luck.

 

To find the velocity at d=10m use

change in displacement = v(initial)t + .5at^2


From there, you can find the velocity at d=40 from

v(final)^2 = v(initial)^2 + 2a(change in displacement)