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# Kinematic, Free Fall. Newton Laws. watch

1. A particle is projected vertically upwards with a speed of 30ms^-1 from a point A. The point B is h meters above A. The particle moves freely under gravity and is above B for a time 2.4s. Calculate the value of h.

I have no idea where to begin.

I appreciate any help.
2. always write out the SUVAT equations and then put in as many numbers as you can...

for this problem you could start at the top.... how long does it take the particle to descend from the top to B ?
3. (Original post by the bear)
always write out the SUVAT equations and then put in as many numbers as you can...

for this problem you could start at the top.... how long does it take the particle to descend from the top to B ?
The problem is that I just know acceleration due to free fall (9.81ms^-2) and time (2.4s)
4. if it spends 2.4 seconds above B that means it spends 1.2 seconds rising from B and 1.2 seconds approaching B from above.

using v = u + at, starting at the top

u = 0

a = 9.8 ( you can keep it positive if you want )

t = 1.2

this gives you v ( downwards ) at the point it moves through B
5. Thanks, I figured it out how to solve it.
6. (Original post by the bear)
if it spends 2.4 seconds above B that means it spends 1.2 seconds rising from B and 1.2 seconds approaching B from above.

using v = u + at, starting at the top

u = 0

a = 9.8 ( you can keep it positive if you want )

t = 1.2

this gives you v ( downwards ) at the point it moves through B
I tried to solve it but the result did not match, but why you set u = 0 and not v = 0
7. (Original post by anasyusef)
I tried to solve it but the result did not match, but why you set u = 0 and not v = 0
if you start at the highest point the initial velocity is zero.

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