Work done against friction for a car with 125 KJ KE.

AI Thread Summary
A 1200 kg car with 125 kJ of kinetic energy ascends a 20-degree slope to a height of 10 m. The gravitational potential energy at the top is calculated as 117,720 J, leading to an energy loss of 7,280 J, which represents the work done against friction. The discussion reveals confusion regarding the interpretation of the height versus distance traveled up the slope. Participants confirm that the energy lost equals the work done against friction if friction is the only energy loss. The thread highlights the importance of ensuring accurate problem details for correct calculations.
Molly1235
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"A 1200kg car as kinetic energy 125kJ at the bottom of a 20 degree slope. It rises to a height of 10m. Calculate work done against friction."

Relevant equations:

Work = force x distance in direction of that force

Work = KE = 1/2 x m x v^2

I'm not really sure where to start...tried several things but haven't got anywhere.

For example:

Work done = KE
125000J = 1/2 x 1200 x v^2
V^2 = 125000/600 = 208.3
V = 14.4 m/s

Or

GPE at top of slope = mgh
1200 x 9.81 x 10 = 117,720

Energy lost = 125000 - 117720 = 7280 J

But neither of these answer the question.

Also tried

Distance traveled = 10/sin20 = 29.24m

So f = 125000/29.24 = 4274.9J buy apparently that's wrong.

Someone please help? :-)
 
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Molly1235 said:
GPE at top of slope = mgh
1200 x 9.81 x 10 = 117,720

Energy lost = 125000 - 117720 = 7280 J
This is the one you want.

If that's not right: Are you sure it says "rises to a height " of 10m? Maybe they meant that it travels up the ramp a distance of 10 m?
 
Doc Al said:
This is the one you want.

If that's not right: Are you sure it says "rises to a height " of 10m? Maybe they meant that it travels up the ramp a distance of 10 m?

I tried it that way as well and none of the answers match up (it's multiple choice). Hm, perhaps I copied the answers/some of the question down wrong!
 
Doc Al said:
This is the one you want.

If that's not right: Are you sure it says "rises to a height " of 10m? Maybe they meant that it travels up the ramp a distance of 10 m?

So just to confirm, would the energy lost be the same as the work done against friction?
 
Molly1235 said:
So just to confirm, would the energy lost be the same as the work done against friction?
Yes, assuming friction is the only source of energy "loss".
 
Molly1235 said:
I tried it that way as well and none of the answers match up (it's multiple choice). Hm, perhaps I copied the answers/some of the question down wrong!

What are the choices?
 
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