- #1

- 442

- 0

a) 1 second

b) 5 seconds

c) What is the maximum height the ball can reach

(Take the acceleration due to gravity to be of 10 m/s)

a) I did: s = ut + 0.5 x at^2

I got 15 m, which I'm pretty sure is correct.

b) For this one, I first tried: s = (20 x 5) + (0.5 x -10 x 5^2) and I got a displacement of 25 m, which, sounds a bit strange since the ball would be traveling at 20 m/s by the fourth second and would hit the ground at 30 m/s.

So I tried the same equation but using the initial velocity 0, and therefore, instead of five, three seconds. With the maths I got 45 m displacement.

Which one is right please so I know how to approach other problems like these better?

And for C, as I looked at it straight away without thinking or doing any maths I thought that the ball would reach a height of 30 m, because for the first second it would move 20 m and for the next second, it would move 10 m (20 m/s decelerated by gravity to 10 m/s). I mean I know it is wrong, but I simply can't get my head around it.

What is getting me confused regarding that is that the ball is only moving at 20 m/s in the very first moment after that, it is already decelerating, but one second later, it would be in fact moving at 10 m/s, right?

Thanks,

Peter.