Power needed to push an object vertical at constant velocity

[IAmPat]

Homework Statement

Stuntman's Freefall, a ride at Six Flags Great Adventure in NewJersey, stands 39.6 meters high. Ignoring the force of friction, what is the minimum power rating of the motor that raises the 1.20×10⁵kg ride from the ground to the top in 10.0 seconds at a constant velocity?

Homework Equations

Constant Velocity = 39.6 / 10 = 3.96m/s
1.20×10⁵ = 120000.0 kg

The Attempt at a Solution

I've tried it two ways now, but clearly neither of them worked.

First way:

$$\Delta$$KE = $$\frac{1}{2}$$ * (1.20×10⁵) * (3.96)²
$$\Delta$$KE = 940,896
W = $$\Delta$$KE
W = 940,896

P = $$\frac{W}{t}$$
P = $$\frac{940896}{10}$$
P = 94089.6 watts

This was wrong... so I tried this way

2nd way:

Velocity = 3.96m/s
Acceleration = .396m/s²
$$\sum$$Fy = (1.20×10⁵) * .396m/s²
$$\sum$$Fy = 47,520

W = F * $$\Delta$$y
W = 47250 * 39.6
W = 1,881, 792

P = $$\frac{W}{t}$$
P = $$\frac{1881792}{10}$$
P = 188179.2 wattsRan out of ideas. What am I missing here?

 

[kuruman]

Constant velocity means ΔKE = zero.

Try power P = Fv where F is the force supplied by the motor. Can you find F?

 

[IAmPat]

Constant velocity means ΔKE = zero.

Try power P = Fv where F is the force supplied by the motor. Can you find F?

Then I end up with the same answer as my second try though. Unless I'm calculating Force wrong?

Velocity = 3.96m/s
Acceleration = .396m/s2
Fy = m*a
Fy = (1.20×105) * .396m/s2
Fy = 47,520

P = F * v
P = (47520)(3.96)
P = 188179.2 watts

 

[Chronos]

You need to convert velocity to acceleration.

 

[kuruman]

You need to convert velocity to acceleration.

I am not sure what this means. If the velocity is constant, the acceleration is zero. Here, we are neglecting friction, so there are only two forces acting on the ride, the lifting mechanism and gravity. If the ride moves at constant velocity, what must the force of the lifting mechanism be equal to?

 

[WatermelonPig]

If sumF = 0 then a = 0. The only forces are gravity and the motor.

 

[kuruman]

Correct-o. Can you figure out then what the force exerted by the motor is?