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practice question

1-calculate the work done by a long distance runner during a 10 km race. The mass of the runner is 52 kg.
gravitational field strength is 9.8N/Kg

2 - suggest a reason why the actual amount of work done is likely to be higher than the calculated value

Reply 1

username3818132

I think you missed the force at which he went....

Reply 2

chrisyabantony14

Original post by neluxsan

I think you missed the force at which he went....

I need to calculate the force first and after the work done I think is why the gave me the gravitational field strength

Reply 3

username3818132

Weight acts downward with G.P.E (Gravitational Potential Energy), which is independent of the work done horizontally. This is because cos90=0.....hence when applied to W=F*D, W=0...so independent....So I think you are missing something....

Reply 4

chrisyabantony14

Original post by neluxsan

that question work out of 3 marks which means that I need to convert the km into metres
calculate the force applied and calculate the work done

Reply 5

phys981

neluxsan is correct - unless this runner is running 10km vertically upwards, then it's not the gravitational force which counts.

Have you given us the full question?

Reply 6

chrisyabantony14

Original post by phys981

neluxsan is correct - unless this runner is running 10km vertically upwards, then it's not the gravitational force which counts.

Have you given us the full question?

yes i did

Reply 7

phys981

Original post by chrisyabantony14

yes i did

Does the question come from a book?

In order to correctly calculate the work done, we need either the horizontal force, assuming he's running horizontally, or we have to assume he's running 10km vertically (which isn't likely as he'd run out of oxygen :wink:

)

Force and distance have to be in the same direction. if they're not, we have to take the cosine of the angle between them as described above. When force and distance moved are at right angles to each other, thereis no work done.

If this is a question that your teacher has made up for you, be gentle when you explain this :smile: