emplar
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i) Calculate loss of GPE from X to Y = 4.66x10^4

ii) Calculate Kinetic energy at Y = 8.55x10^4

iii) The total distance travelled by the motorbike from X to Y along the ramp is 120 m. Calculate the average accelerating force that the motorbike engine provides along the ramp.

Work done = Fd so F = work done/d

Im confused on why you're supposed to subtract the value for i) from ii)
I know that the loss in GPE is equal to the gain in kinetic energy.
But why cant you just use the kinetic energy from ii) for the work done?
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uberteknik
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(Original post by emplar)
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i) Calculate loss of GPE from X to Y = 4.66x10^4

ii) Calculate Kinetic energy at Y = 8.55x10^4

iii) The total distance travelled by the motorbike from X to Y along the ramp is 120 m. Calculate the average accelerating force that the motorbike engine provides along the ramp.

Work done = Fd so F = work done/d

Im confused on why you're supposed to subtract the value for i) from ii)
I know that the loss in GPE is equal to the gain in kinetic energy.
But why cant you just use the kinetic energy from ii) for the work done?
There are two forces acting on the motorbike to achieve the 30m/s speed at the end of the ramp:

1) Acceleration due to gravity which converts the G.P.E. component to K.E.

2) Acceleration due to the engine of the motorbike which adds to the K.E. from 1)

So the K.E. @ 30m/s = K.E.gravity + K.E.engine

Simples.
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emplar
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(Original post by uberteknik)
There are two forces acting on the motorbike to achieve the 30m/s speed at the end of the ramp:

1) Acceleration due to gravity which converts the G.P.E. component to K.E.

2) Acceleration due to the engine of the motorbike which adds to the K.E. from 1)

So the K.E. @ 30m/s = K.E.gravity + K.E.engine

Simples.
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They have taken away the values, whereas you're saying they should be added?
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uberteknik
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(Original post by emplar)
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They have taken away the values, whereas you're saying they should be added?
No.

Rearrange my expression for K.E.

Ek total = Ek engine + Ek gravity

Ek engine = Ek total - Ek gravity

i.e. the question wants the work done by the engine alone and not the combined contribution from the engine and gravity.
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emplar
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(Original post by uberteknik)
No.

Rearrange my expression for K.E.

Ek total = Ek engine + Ek gravity

Ek engine = Ek total - Ek gravity

i.e. the question wants the work done by the engine alone and not the combined contribution from the engine and gravity.
Ahh thank you, that makes so much sense now!
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