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I have no clue about this PROBLEM!!!?

I have no clue about this PROBLEM!!!? - Physics Forum

I have no clue about this PROBLEM!!!? - Physics Forum. Discuss and ask physics questions, kinematics and other physics problems.


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Old 06-26-2009, 10:16 AM
Pipette Filler
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Default I have no clue about this PROBLEM!!!?



Can anyone give me detailed description of how to this and what formula to use?
Thank you so much for the help!


A block with mass m = 15.6 kg slides down an inclined plane of slope angle 14.7o with a constant velocity. It is then projected up the same plane with an initial speed 2.80 m/s. How far up the incline will the block move before coming to rest?
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Old 06-26-2009, 10:18 AM
Pipette Filler
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The missing piece is the frictional force of the block against the plane. The first part of the problem lets you find that value:

If the block moves at constant velocity, the friction force Fr is equal to the force (gravity) pulling the block down. The gravity force on the block is m*g*sin?; therefore Fr = m*g*sin?.

You can solve the second part in two ways: energy conservation or mechanics. I prefer energy conservation:

Initial energy of the block = KE = 0.5*m*v0. The block will rise on the plane until that energy is used by friction and gravitation potential energy.

Friction energy used is Fr*L, where L is the distance along the plane
Gravity potential = m*g*h, where h is the altitude at the end of travel. If L is the distance traveled, h = L*sin?. So the total energy used going up the plane is

Fr*L + m*g*L*sin? and this is equal to 0.5*m*v0. Then using Fr from the first part,

m*g*L*sin? + m*g*L*sin? = 0.5*m*v0

g*L*sin? + g*L*sin? = 0.5*v0

L*2*g*sin? = 0.5*v0

L = 0.25*v0/(g*sin?)
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