Conservation of Mechanical Energy

AI Thread Summary
The discussion focuses on a physics homework problem involving a 1.0 kg projectile launched at a 45° angle with an initial velocity of 30 m/s. Key concepts include the conservation of mechanical energy, where total mechanical energy is the sum of kinetic and potential energy. The participant is uncertain about how to apply the equations for kinetic energy (KE) and potential energy (PE) to find the kinetic energy at the highest point and the work done in firing the projectile. The response emphasizes understanding projectile motion principles to solve the problem effectively. Clarification on the missing values and application of relevant equations is sought for a complete solution.
domtar
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Homework Statement



A 1.0 kg projectile is fired from a point on the Earth's 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.
 
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Hi domtar,

The keyword is "projectile". What do you know about projectile motion?

ehild
 
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