if a engine has to work 100 joule and the effect is 25w how long does it take ?

Guest Nov 5, 2015

#1**+15 **

I'm assuming you mean the __power__ of the engine is 25 W. "effect" is a very broad term.

Power is rate at which work can be done, shown by its formula below:

\(P=\frac{w}{t}\)

P is power, w is work, and t is time. We'd use the equation for the power and work in your question.

\(25=\frac{100}{t}\)

\(t=\frac{100}{25}\)

\(t=4s\)

The engine would take 4 seconds.

Will85237 Nov 5, 2015

#1**+15 **

Best Answer

I'm assuming you mean the __power__ of the engine is 25 W. "effect" is a very broad term.

Power is rate at which work can be done, shown by its formula below:

\(P=\frac{w}{t}\)

P is power, w is work, and t is time. We'd use the equation for the power and work in your question.

\(25=\frac{100}{t}\)

\(t=\frac{100}{25}\)

\(t=4s\)

The engine would take 4 seconds.

Will85237 Nov 5, 2015

#3**0 **

**Thanks Will, **

**and welcome back to the forum after all this time.**

**It is really great to see you again.**

I have never understood much physics but every now an again I get inspired to try and understand.

I am a mathematicican so I like to understand the units. Not just the remember the formula.

**This answer is only for my own benefit. Will's answer is excellent.**

-----------------------------------------

Now a **Watt is a unit of power** and ( I googled this)

\(1W=1Kg\; m^2/s^3 = 1 \;Kg\;(ms^{-2})\;s^{-1} \qquad = \frac{1\;Kg\;m^2}{s^{-3}}\)

Now I think this means that 1W = the force needed to increase the acceleration of a mass 1Kg every second. I assume that this is in a vacuum.

Please correct me if I am wrong.

I also googled Joule.

The joule (/ˈdʒuːl/), symbol J, is a derived unit of energy in the International System of Units. It is equal to the energy transferred (or work done) to an object when a force of one newton acts on that object in the direction of its motion through a distance of one metre (**1 Joule = 1 newton metre or N. · m**).

ok I better google Newton now

**One newton is the force needed to accelerate one kilogram of mass at the rate of one metre per second squared.**

** 1 Newton = 1Kg m/s ^{2}**

so we have

FORCE unit 1 Newton = 1Kg m/s^{2}

WORK unit = 1 Joule = FORCE * METRES = Newton Metres = 1Kg m/s^{2 }* m = 1Kg m^{2}/s^{2 }

POWER UNIT = 1 WATT = WORK/SEC = NEWTONS/SEC = 1Kg m^{2}/s^{3}

Ok..............

so

**force (Newtons) mass* acceleration **

**work (joules) is force exerted times by distance**

**power (watts) is how much work is done every second**

if a engine has to work 100 joule (work) and the effect is 25w (power) how long (time) does it take ?

Power is how much work is done every second so that must equal 100/s

so

power = work/time

25 = 100/t

25t = 100

t = 4 seconds

I wish I could remember this stuff. ://

Melody Nov 6, 2015