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1.Power is defined as W / t. But problem is that the work done by the force increases with displacement, since body travels same distance in ever shorter time periods. So how can we find instantaneus power if the more time it passes by more work does force do in same time interval ?

2.

P = W/t = F * s/t = F * s/t = F * v

I understand how we derived this formula but have no clue why it's legit.

For one thing v is average speed over distance s, so why can we use it in formula to get power?

I'm sorry for not being able to articulate my question any better(),

but I do hope someone will be able to figure out what I'm trying to ask and explain it .

3.Is P = F * v instantaneus power? If so, why would this formula give us instantaneus power?

4.Most machines are designed and built to do work on objects. These machines are described by a power rating. The power rating indicates the rate at which that machine can do work upon other objects. Thus, the power of a machine is the work/time ratio for that particular machine. Over what period of time is work measured for that machine?

Even if machine has power rating of 10kW/1 day, wouldn't in two days of non-stop running have even greater power?

I'm also aware that this can't go on for ever, since rotor or whatever at some point reaches its final speed and thus can no longer accelerate and have its kinetic energy changed. What happens then? Is at that moment power=zero?

thank you

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# Homework Help: Average and instantaneous power-please help

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