Calculate Change in Kinetic Energy for Masses on Pulley

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The discussion focuses on calculating the change in kinetic energy (DKE) for a 45 kg mass moving on a ramp connected to a 103 kg hanging mass via a frictionless pulley. The coefficient of kinetic friction is 0.250, and the ramp angle is 37 degrees. The initial approach involved determining the velocity using a derived equation, but the calculated DKE of 5059.76 J was deemed incorrect. Participants suggest checking the signs of the terms in the equations used, indicating potential errors in the calculations. The conversation emphasizes the importance of accurate sign conventions in physics problems.
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Two masses are connected by a string via a pulley, m1=45kg is on a ramp while m2=103kg is hanging off the edge. The pulley is frictionless and of negligible mass. The coefficient of kinetic friction between the 45.0 kg block and incline is 0.250. Determine the change in the kinetic energy of the 45.0 kg block as it moves from A to B, a distance of 20.0 m. Theta is 37 degrees


I first tried to find velocity (V) to use in a DKE equation
D=delta

My equation for V was sqrt((2(m2ghi-m1ghf+um1gdcos@))/(m1+m2))

u = coefficient of kinetic friction
hi = initial height, 20m in this case
hf = 20sin@
@ = theta

I then used DKE = 0.5m1Vf^2-0.5m1Vi^2

where Vi = 0

Using this method I got an answer of DKE of 5059.76J, which was wrong.
I do not know if I am over simplifying the problem or thinking too much or if I'm completely thinking in the wrong direction. Help would be much appreciated.
 
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asianguy361 said:
My equation for V was sqrt((2(m2ghi-m1ghf+um1gdcos@))/(m1+m2))
Check the signs of your terms.
 
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