# EnergyWatch

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#1

i) Loss GPE = 0.59

iii) Calculate the kinetic energy of the glider at this velocity of 1.8 m s^–1. kinetic energy = 0.41 J

(iv) Explain why the answer to (b)(iii) is not the same as (b)(i)

I dont understand this answer to this question. I talked about friction, however the answer to this question is that "they have not taken into account the kinetic energy of the 0.1kg mass"??
0
1 year ago
#2
Kinetic energy gained = GPE lost

You've worked out the kinetic energy of the glider, but the GPE of the mass is converted into kinetic energy of the mass AND glider as it falls.
The GPE lost is equal to the kinetic energy gained by the mass and glider system, so clearly from this you can see that to actually work this out, the mass would be (mass of glider + 0.1kg) hence the kinetic energy gained would be greater than the kinetic energy of the glider, which is why the reading you got was lower.

Sometimes it can be helpful to take it off the pulley. The mass of the 'stuff' that's moving is both the mass of the 0.1kg mass and the mass of the glider rather than just the glider.

Also i would have expected them to say that the pulley was frictionless but as it says that the track is frictionless, use this to draw the conclusion that friction won't be an accepted answer.
1
#3
(Original post by Graphittte)
Kinetic energy gained = GPE lost

You've worked out the kinetic energy of the glider, but the GPE of the mass is converted into kinetic energy of the mass AND glider as it falls.
The GPE lost is equal to the kinetic energy gained by the mass and glider system, so clearly from this you can see that to actually work this out, the mass would be (mass of glider + 0.1kg) hence the kinetic energy gained would be greater than the kinetic energy of the glider, which is why the reading you got was lower.

Sometimes it can be helpful to take it off the pulley. The mass of the 'stuff' that's moving is both the mass of the 0.1kg mass and the mass of the glider rather than just the glider.

Also i would have expected them to say that the pulley was frictionless but as it says that the track is frictionless, use this to draw the conclusion that friction won't be an accepted answer.
Thank you a lot mate, I understand it now!
1
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