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**They****Member**- Registered: 2017-01-02
- Posts: 2

A man of mass 65 kg is holding a bucket of mass 15 kg. He walks 50 m on a level road at a constant speed

3 m/s and then climbs up a hill of height 20 m. What is the work done by the man ?Explain also... .......

They they

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**bob bundy****Administrator**- Registered: 2010-06-20
- Posts: 8,137

hi They,

Welcome to the forum.

I've thought about this since I read it this morning and I had a look on a physics forum. Work done is defined as force x distance moved. For the up move that's the same as gain in potential energy and is given by the formula mgh = mass x acceleration due to gravity x height. The horizontal movement is much more complex. As the velocity is constant there's no force of acceleration and friction between the ground and the man's shoes has no movement and so is zero. That might suggest that no work is being done.

But that cannot be correct or we'd all be able to walk for ever. Every muscle involved is doing work, moving tendons and thence bones. Also walking requires an increased heart and breathing rate so more work there. The amount of work is impossible to calculate. I suspect that even with a treadmill and a mask to measure oxygen intake only a rough approximation is possible.

Try this; walk normally for a while. Then repeat but this time raise your knees as high as you can for each step and swing your arms wildly. Feeling any different? The second involves much more work, but how would you compute this?

If this is homework ask your teacher about the man's build. leg length, muscle tone, fitness regime etc etc. That should keep them happy.

Bob

ps. I've looked at your other post but I cannot understand what the first question is asking for. Something odd about the notation when I view it. Sorry.

Children are not defined by school ...........The Fonz

You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei

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