Mechanics - Projectiles - Terribly Stuck!

Use g= 10ms-2

A firework is buried so that its top is at ground level and its projects sparks all at a speed of 8ms-1. Air resistance may be neglected.

Calculate the height reached by a spark projected vertically and explain why no spark reach a height greater than this.

I've tried answering this question but I just get a height of 8m; however this is the wrong answer. Can some please explain which SUVAT equation I need to use and why

Reply 1

D-Day

You know at maximum height it's velocity will be zero. You know it's initial velocity. You know acceleration. That is three of four parts of

S^2=So^2+2a(Yf-Yo)

Reply 2

high_maintenance_girl

D-Day

You know it's initial velocity.

I do?
I didn't think I did.
I've just tried it with zero and thats not working out either.

Reply 3

D-Day

high_maintenance_girl

I do?
I didn't think I did.
I've just tried it with zero and thats not working out either.

high_maintenance_girl

and it projects sparks at a speed of 8ms-1

You do.

Reply 4

imtired

D-Day

You know at maximum height it's velocity will be zero. You know it's initial velocity. You know acceleration. That is three of four parts of

S^2=So^2+2a(Yf-Yo)

that's usually written as

v^2 = u^2 + 2as

, if it makes it any simpler. you've got a, u and v, you need s.

Reply 5

D-Day

imtired

that's usually written as

v^2 = u^2 + 2as

, if it makes it any simpler. you've got a, u and v, you need s.

Different country, different letters apparently. Forgive my not being British :p:

Reply 6

high_maintenance_girl

D-Day

You do.

I see I see. I just need things spelling out to me lol :p:

But I still got a problem

v = 0
u = 8
a = - 10

Using v = u + at, that gives time to reach max height as 0.8 seconds

Then if i substitute all those values into s = ut + (0.5 x a x t^2)
I get 3.2 - 3.2 = 0 :s-smilie: