- #1
Foopyblue
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Homework Statement
A box slides down an inclined plane (angle = 37*). The mass of the block is 35 kg, the coefficient of kinetic friction between the box and the ramp is 0.3, and the length of the ramp is 8 m. If it starts from rest at the top of the ramp, with what speed does it reach the bottom? Use energy equations.
Homework Equations
[/B]
[itex]Work = \Delta K [/itex]
[itex]Work = \Delta E [/itex]
[itex]Work = \Delta K + \Delta U_g + \Delta E_t{}_h[/itex]
The Attempt at a Solution
I understand how to do this with motion equations:
VF2 = Vi2 +2ad
VF2 = 2ad
a = gsin(θ)-(FFR/m)
a = gsin(37) - (350cos(37)*0.3/35)
a = 6-2.4
VF2 = 2 * 3.6 * 8
VF2 = 57.6
VF = 7.6
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But I am at lost with energy equations
I calculated the Net Work of the system by calculating the Work of each Force and adding them together and I got 1020 J.
I want to plug this into either one of these equations:
[itex]Work = \Delta K [/itex]
1020 = (1/2)mv2
[itex]Work = \Delta K + \Delta U_g + \Delta E_t{}_h[/itex]
1020 = (1/2)mv2 + mgy + FFR * d
But what I don't understand is how the first equation can be equal to the second equation. Wouldn't I get a different answer? Why is the change in kinetic energy alone enough to demonstrate the change in all of the energies?
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