A particle is projected vertically upwards at 30 m/s. Calculate (a) how long it takes to reach its maximum height, (b) the two times at which it is 40 m above the point of projection, (c) the two times at which it is moving at 15 m/s.
2. Homework Equations [/b
final velocity (v)
initial velocity (u)
acceleration due to gravity (a) = 10m/s^2
Distance or displacement (s)
v^2=u^2 + 2as
The Attempt at a Solution
I first find the maximum height, this is where i used the equation v^2=u^2 +2as
0^2=30^2 + 2(10)s
s=45 m maximum height
then i used that value and plugged into the equation to find time
45= 1/2 (30+0)t
therefore total time is 3 seconds for the particle to reach its maximum height.
part (b) is where i am stuck
however i move on to part (c)
and i plugged in the values in the equation
however the question asked for two (2) times. so i am also stuck with finding the second time...