course Phy 201
I am having trouble working through this problem, can you help. Seems like I've done this before, but I'm drawing a blank.
A block of mass 1.8kg is held stationary on a level frictionless tabletop. A mass of .2kg is attached to the block by a string over which runs horizontally from the block to a pulley located at the edge of the table; the mass hangs freely from the string over the pulley.As the hanging mass descends 3.2m from rest the block is pulled 3.2m along the tabletop. How much work does gravity do on each mass during the process?
The 1.8kg mass is under 9.8m/s^2 of gravity, the table is exerted enough force to hold the mass therefore it must be exerting 9.8m/s^2, therefore, force of the 1.8kg object is 0.
Right idea, but your statement needs a little patching up:
The 1.8kg mass is under a force of 1.8 kg * 9.8m/s^2 of gravity, the table is exerted exerts enough force to hold the mass therefore it must be exerting a force of 1.8 kg * 9.8m/s^2, therefore, force of on, not of the 1.8kg object is 0.
Work on 1.8kg mass = 1.8kg*9.8m/s^2=17.6N
this is the force of gravity; it's not work
Work on .2kg mass = .2kg*9.8m/s^2 = 1.96N
this is the force of gravity; it's not work
Using the definition of KE, determine the velocity of the system after having traveled the 3.2m?
You know the force exerted by gravity on each object. You know the force exerted by the table on the first.
The net force on the system is therefore the 1.96 kg force exerted on the suspended mass.
The system moves in the direction of that force. How far does it move, how much work does the force therefore do, and by how much does the KE of the system therefore change?
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