# Velocity from a catapult

I-Love-Maths2
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A catapult is pulled back 10cm with a force of 30N. How fast does the stone of mass 0.5kg got at maximum speed assuming no air resistance.

I have absolutely no idea how to do this...
But, I am assuming you use Ek=1/2mv^2, though I can't figure out how to apply it

To rearrange that:
V=sqrt[Ek/(1/2m)]

So, to make it clearer
- 10cm would be the displacement (s)
- 30N would be the force (F)
- 0.5kg would be the mass (m)
- 9.8m/s is the given unit for gravity in GCSE (g)

Other equations that might be useful:
- WD=Fs so WD=300J
- Ep=mgh
- W=mg

So from that we need an equation that uses WD and m

Can anybody help?

Last edited:

Homework Helper
How much force will be applied to the stone - and over what distance?
I think we are supposed to assume that the parts of the catapult have zero mass...
and that the catapult is immovable.

Homework Helper
WD=Fs so WD=300J
what becomes of WD once the projectile is away ?

By the way, you do have an error in there ...

I-Love-Maths2
Keep this down to GCSE standard please
Does WD=Ek according to the conservation of energy?