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## Homework Statement

A 1.0 kg projectile is fired from a point on the earths surface at an angle θ = 45° with the horizontal and with an initial velocity v = 30 m/s. Neglect any effects due to air resistance and find:

a) What is the kinetic energy of the projectile when it reaches the highest point on its trajectory?

b) How much work was done in firing the projectile?

## Homework Equations

total mechanical energy = KE + PE

KE_i + PE_i + W = KE_f + PE_f

## The Attempt at a Solution

I'm not sure how to start this problem, or how to tackle it. I'm assuming I have to use the second equation? I let KE = 1/2 mv^2, m=1.0kg, v=30m/s. Then PE=mgh, m=1.0kg, g=9.81m/s/s, h=?. Then W=Fdcosθ, F=?, d=? cosθ=cos45°. Then I'm sort of stuck... There's a lot of values missing and I'm not sure how to solve or where to start.

Any help would be appreciated, thank you.