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secondary 4 | Physics
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Hi, I am in a dilemma
Can someone explain why for the question on top, there is work done against the frictional force?
Looking at the guide below to use its theory on top , doesn't the box's weight act downwards , making the work done by the weight 0?
Date Posted: 7 years ago
Views: 496
Hey Darren,
Work done against friction means the the work done when the force used to overcome friction is moved over a distance.
Let's assume that the weight of the box is 100N.
When the box is dropped over a distance of 3m, the box loses GPE: 3 X 100 = 300J.
Due to conservation of energy, this 300 cannot be gone. In this case, the most likely energy conversion must be
1)KE of the boxes since the box les started moving from rest
2)heat created due to friction between the box and the surface
3)other energy losses eg. due to air resistance, which is this case let's assume its negligible.
Hence energy conversion is
GPE to KE of box and heat due to friction.
Work done against friction is referring the energy loss due to friction, which is the heat. Hence the work done against friction is
10 X 4 = 40N.
So the remaining energy must have been converted to the KE of the boxes.
Hope this helps, Darren.
Work done against friction means the the work done when the force used to overcome friction is moved over a distance.
Let's assume that the weight of the box is 100N.
When the box is dropped over a distance of 3m, the box loses GPE: 3 X 100 = 300J.
Due to conservation of energy, this 300 cannot be gone. In this case, the most likely energy conversion must be
1)KE of the boxes since the box les started moving from rest
2)heat created due to friction between the box and the surface
3)other energy losses eg. due to air resistance, which is this case let's assume its negligible.
Hence energy conversion is
GPE to KE of box and heat due to friction.
Work done against friction is referring the energy loss due to friction, which is the heat. Hence the work done against friction is
10 X 4 = 40N.
So the remaining energy must have been converted to the KE of the boxes.
Hope this helps, Darren.
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