Projectile Motion question (1 Viewer)

[deswa1]

Hey guys,

This question is from Surfing Physics and I've got no clue how to solve it...

A projectile fired up into the air from the top of a 75m high cliff hits the ground 500m out from the base.

Find the initial velocity, time of flight and maximum height.

If anyone can give a worked solution, it would be greatly appreciated

 

[bleakarcher]

In this situation, you can not determine the initial velocity, time of flight, maximum height as a numeral, only in terms of variables

 

[hscishard]

Prob was fired horizontally and not up into the air so max height was just the cliff. If so you can find the time of flight first, then you can determine the initial velocity by considering the range.

Is that the exact question but? if so, bleakarcher is right on the variables

 

[bleakarcher]

it was fired up into the air lol. if it was horizontally fired:

Let the intial velocity be V and time of flight be T.
S(x)=u(x)t
When t=T, S(x)=500,
T=500/u(x)
S(y)=u(y)t+(1/2)a(y)t^2
S(y)=u(y)t-4.9t^2, where g=-9.8m/s^2
When t=T, S(y)=-75,
u(y)T-4.9T^2=-75
As T=500/u(x),
500u(y)/u(x)-4.9*500^2/u(x)^2=-75
Assuming the projectile is shot horizontally:
u(x)=Vcos0=V, u(y)=Vsin0=0
Hence:
4.9*500^2/V^2=75
V=sqrt[4.9*500^2/75]=127.8m/s

 

[deswa1]

Thanks guys, I thought there was no way to work it out. The answer was velocity is 65 ms at 39.7 degrees so there must be something missing like time of flight. That was the question word for word BTW.

Cheers