Calculating Force Needed to Lift 79kg Mass at Const. Speed

[daltomagne]

A woman raises herself in a bucket. How hard must she pull downward to raise herself slowly at constant speed? The mass of the person plus the bucket is 79 kg.

m=79kg
g=9.8m/s^2 (downward)

i know $$\Sigma$$F=ma so i end up with 774.2 N. I'm a little lost as where to go now.

 

[fizzynoob]

Sum the forces in the y direction, if speed is constant that acceleration is zero

Forces in y =Fp- Fg = 0

Solve for fp

 

[Olly4]

You actually already solved it. For something to move at a constant speed, the net force has to be 0. So she just has to pull hard enough to overcome the gravitational force. Which you already calculated.

 

[Doc Al]

You need to understand how she is raising herself. A simple rope and pulley arrangement? A diagram would be helpful.

 

[rwisz]

I would first like to commend you for using the correct formula, ΣF=ma, to calculate the force needed to lift the 79kg mass at a constant speed. Your calculation of 774.2 N is correct.

To answer the question of how hard the woman must pull downward to raise herself slowly at constant speed, we need to consider the forces acting on the system. In this case, the only forces present are the gravitational force (weight) of the woman and the bucket, and the force exerted by the woman pulling on the bucket.

Since the woman is raising herself at a constant speed, we can assume that the net force acting on the system is zero, as there is no acceleration. This means that the force she exerts by pulling down on the bucket must be equal in magnitude to the weight of the system, which is 774.2 N.

In other words, the woman must pull down with a force of 774.2 N to counteract the weight of the system and raise herself at a constant speed. This is because the two forces are in equilibrium, resulting in a net force of zero.

It is important to note that this calculation assumes ideal conditions, such as a frictionless pulley system and no other external forces acting on the system. In reality, there may be other factors that could affect the force needed, such as the friction between the bucket and the pulley or the strength and technique of the woman pulling on the bucket.

In conclusion, the force needed for the woman to raise herself slowly at a constant speed is 774.2 N, which is equal in magnitude to the weight of the system. This is due to the equilibrium of forces in this scenario.