
#1
Feb1308, 10:00 AM

P: 54

1. The problem statement, all variables and given/known data
Draw and label a graph with energy for the y axis and displacement for the x axis of the kinetic energy and potential energy of an object in freefall that started with a horizontal speed of 30 m/s from a height of 80 m. 2. Relevant equations U=mgh k=1/2mv^2 3. The attempt at a solution I drew a straight line with negative slope for potential energy because m and g are constants in U=mgh, so it should be a linear graph, as for kinetic energy, I am sitting on the fence on whether or not to draw a straight line or a curve The v^2 makes me want to draw a curve, however, if the the potential energy is a straight line and K = E  U, then shouldn't k be directly proportional to displacement as well? 



#2
Feb1308, 10:12 AM

Mentor
P: 40,906

Why not use a bit of kinematics to double check? What's the relationship between v (or v^2) and displacement for a falling object? 



#3
Feb1308, 11:28 AM

P: 54

ahh..
v^2=v0^2+2a(xx0) but since initial velocity in the y direction is 0 v^2=2g(xx0) and since 2g is a constant, v^2 is directly proportional to displacement, and thus kinetic energy is directly proportional to displacement! Thanks Doc Al! 


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