Minimum Power Needed to Accelerate Air from Rest to 15 m/s

[arpsachin2]

Homework Statement

A fan accelerates 2 m^3/min of air from rest to a velocity of 15 m/s. If the density of air is 1.25 kg/m^3, determine the minimum power that must be supplied to the fan?

Homework Equations

The Attempt at a Solution

Need some hints or something.

 

[tiny-tim]

welcome to pf!

hi arpsachin2! welcome to pf!

(try using the X² icon just above the Reply box )

hint: momentum

 

[arpsachin2]

Thank you.

Okay a bit more I guess. :(

 

[chemisttree]

You can convert the volume of air to mass using density.

 

[tiny-tim]

(just got up :zzz: …)

force = rate of change of momentum

power = force times … ?

 

[arpsachin2]

Power = force * velocity

Am I heading the right way?Fan accelerates at 2m^3/60 secs to 15 m/s

And density is 1.25kg/m^3.

So is it Power = 1.25kg/m^3 * Acceleration?

How do I get the acceleration?

 

[tiny-tim]

hi arpsachin2!

Power = force * velocity

Am I heading the right way?

yes

Fan accelerates at 2m^3/60 secs to 15 m/s

And density is 1.25kg/m^3.

So is it Power = 1.25kg/m^3 * Acceleration?

and now you've totally lost me!

you don't need the acceleration!

you only need the force, and you can get that from the change in momentum

 

[arpsachin2]

if possible could you show me an example or something?

Thanks

 

[arpsachin2]

hi arpsachin2!


yes


and now you've totally lost me!

you don't need the acceleration!

you only need the force, and you can get that from the change in momentum

Hey,

would it be possible to chat on Gmail or yahoo or something?
Please

 

[arpsachin2]

hi arpsachin2!


yes


and now you've totally lost me!

you don't need the acceleration!

you only need the force, and you can get that from the change in momentum

So change in momentum is

Final momentum - Initial Momentum right

So, would it be 15 m/s - xxxx?

 

[tiny-tim]

hi arpsachin2!

(just got up :zzz: …)

So change in momentum is

Final momentum - Initial Momentum right

So, would it be 15 m/s - xxxx?

15 m/s is a speed, you need a momentum (= mass times speed), in kg m/s,

and then you need a rate of change of momentum, in kg m/s²