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Total energy help

  • Thread starter fball558
  • Start date
1. Homework Statement

it is a multi part problem i found most just need help on last two but gave answers to the ones i found because they are needed to determin the answer.

What is the translational kinetic energy of the real system, at the instant shown in the right diagram?
Ktrans = 10.412 J

What is the distance through which the gravitational force acts on the real system? .19 m

How much work is done on the system by the gravitational force?
Wgrav = -16.758 J

What is the distance through which your hand moves? .72 m

How much work do you do on the real system?
Whand = 102.96 J

At the instant shown in the right diagram, what is the total kinetic energy of the real system?
Ktotal = J

What is the rotational kinetic energy of the machinery inside the box?
Krot,f = J

2. Homework Equations
from a question earlier on my assingment i found that only
translational and rotational kenetic energy are pressent
will need conservation of energy
delta(E) = W + Q
i assumed Q = 0 because we have not went in depth about heat trasfer due to friction and all that stuff.

3. The Attempt at a Solution
 
oops i forgot to show my work ok here is what i did.
inital state box has no energy it is on the ground and not moving.
final state it is .19 meters above the ground moving in +y direction and spinning

i took delta(E) = w + Q Q=0
so delta(E) = W
W would equal work done by your hand (102.96) plus work done by gravity (-16.758) since gravity is - it is actually suptracting so i get delta(E) = 86.202
that sould be total energy but we only want kenetic energy so i found potential energy using mgh (mass was given as 9 kg) so 9*9.8*.19 = 16.758. that should be potential so
i subtracted that from total 86.202 - 16.758 = 69.444
that is my answer but it says im wrong. any help would be great!!
thanks and sorry about the lenght of this post.
 

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