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Constant Power

by Fluent
Tags: constant, power
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Fluent
#1
Nov24-08, 08:37 PM
P: 7
A constant direction force delivers a constant power of 45.0 W to an 8.00-kg mass which is
initially moving in the direction of the force. At t = 0 s, the force is 5.00 N.
Calculate the speed of the mass after 4.00 s.

I've tried to do several different things, however I believe you need to integrate. My intregration skills are really weak, so please don't assume I'll know what you're doing if you skip alot of steps.

Thanks.
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LowlyPion
#2
Nov24-08, 09:24 PM
HW Helper
P: 5,341
Welcome to PF.

You're in luck. You won't need to integrate.

But you will need to understand what power is.

Like what units is power expressed in?
Fluent
#3
Nov24-08, 10:10 PM
P: 7
Kg m^2/s^3

Few more points would be helpful.

Thanks

LowlyPion
#4
Nov24-08, 10:44 PM
HW Helper
P: 5,341
Constant Power

OK and how is power related to Force?

Power = Force times ...?
Fluent
#5
Nov24-08, 11:02 PM
P: 7
velocity.. however unfortunately the answer is not 9 m/s. The other information is needed to solve this.. as the force isn't the same throughout.. (it's 5.00 N only at t = 0 s)
LowlyPion
#6
Nov24-08, 11:09 PM
HW Helper
P: 5,341
You are jumping ahead a bit.

The 9 m/s is the speed at t=0 however.

Now think about what is a watt? A Joule/sec perhaps?

And how many seconds? So how many Joules were added to the energy of the mass? ...

And how many joules of energy did the mass have at t=0? And added together as Kinetic energy how fast does that mean the mass is going?
Fluent
#7
Nov25-08, 04:12 PM
P: 7
Ahh thanks alot man.. appreciate it.


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