Force and Power Required to Lift an Elevator Car

[Lori]

Homework Equations

P = W*V
F_net = ma
V = 3.0 m/s
W = 29.9[/B]

The Attempt at a Solution

I think i got this wrong, but I want you to check if my answer is right :(

Heres what i did:

So,

P = force * velocity
P =force*3.0 m/s

force = force due to gravity + acceleration (net force) is F = ma = 29.9??

P = (29.9*3) = 89.6 kW

 

[haruspex]

force = force due to gravity + acceleration

Yes

= 29.9??

Isn't that just the given mg?

 

[Lori]

Yes

Isn't that just the given mg?

Yeah! That's why I'm unsure of my answer :*(

 

[haruspex]

Yeah! That's why I'm unsure of my answer :*(

So what additional force is required to produce the acceleration?

 

[Lori]

So what additional force is required to produce the acceleration?

Would it be Faddition - 29.9 = m*a where m = 29.9/9.81
so Fadditional = 32.94

Do i use the Fnet to calculate the power or the Fadditional? I think i would have to use P = Fadditional * velocity because I'm trying to find the power of the motor specifically, so the force it should do is Fadditional right? I get the answer 98.8 which is one of the answers!

 

[haruspex]

Would it be Faddition - 29.9 = m*a where m = 29.9/9.81
so Fadditional = 32.94

Not sure how you are defining Faddition there. I intended it to mean the extra force, beyond matching gravity, needed to produce the acceleration. Is that how you are defining it? It does not seem so.

Do i use the Fnet to calculate the power or the Fadditional?

The motor does not understand gravity. All it "understands" are the force it exerts and the speed with which it reels in the cable.

 

[Abhishek kumar]

First calculate force required to produce upward acceleration of 1m/s^2 then u can easily calculate power.

Would it be Faddition - 29.9 = m*a where m = 29.9/9.81
so Fadditional = 32.94

Do i use the Fnet to calculate the power or the Fadditional? I think i would have to use P = Fadditional * velocity because I'm trying to find the power of the motor specifically, so the force it should do is Fadditional right? I get the answer 98.8 which is one of the answers!

 

[Lori]

First calculate force required to produce upward acceleration of 1m/s^2 then u can easily calculate power.

The force upwards is 32.95 I found, so if I multiply it by 3 will I get the power output?

 

[haruspex]

The force upwards is 32.95 I found, so if I multiply it by 3 will I get the power output?

Yes.

 

[Abhishek kumar]

Y

The force upwards is 32.95 I found, so if I multiply it by 3 will I get the power output?

Yes u had done it