PLEASE help on this Mechanics (M1) question... Do you know how to do it??

Question

4) A ball is thrown vertically upwards with a speed of 10ms. Find (a) the highest point it reaches. (b) the total time it is in the air.

The answer to part a i have got as 5.10m which is correct.

However i don't know how to get (b).
The answer in the back of the book for that is 2.04 seconds but i don't know how they got that. PLEASE helpppppppppppppp...

Answer 1

e=-1/2gt^2+10t
-gt+10= 0 so t= 10/9.8=1.02 (time to reach the highest point)
so e= 5.10m
The time to go up is the same to go done so t= 2.04 s
You can sea it writing the equation starting from the maximum height
5.10 =1/2 gt^2
as there the velocity is 0
t = sqrt(10,2/g)=1.02 s(time to go down)