Calculating force required for lifting

In summary, when considering a 240kg mass being lifted by two symmetrical cables, each cable must produce 120g of force to lift the mass. However, the resultant force will always sum to zero, regardless of whether the mass is stationary, being lifted at a constant speed, or being lowered at a constant speed. To accelerate the mass upwards from 0m/s to 2m/s in 3 seconds, an additional force of 160N must be applied to the cables, resulting in a total upward force of 240g + 160N. The laws of motion, specifically the first and second laws, dictate the behavior of the mass in this scenario.
  • #1
sozener1
19
0

Homework Statement


say you have a 240kg rectangular mass

it is pulled upwards by two cables symetrically

since force due to gravity is 240g so each cables would have to produce 120g each to lift the mass.

but the resultant force sum to zero

so if we were just given a FBD of the 240kg mass with two cables attached how would we know it is being lifted up??




Homework Equations





The Attempt at a Solution

 
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  • #2
hi sozener1! :smile:
sozener1 said:
so if we were just given a FBD of the 240kg mass with two cables attached how would we know it is being lifted up??

the forces (and the FBD) will be the same no matter whether the mass is stationary, is being lifted up at constant speed, or is being lowered at constant speed :wink:
 
  • #3
tiny-tim said:
hi sozener1! :smile:


the forces (and the FBD) will be the same no matter whether the mass is stationary, is being lifted up at constant speed, or is being lowered at constant speed :wink:


so if you want to accelerate the mass upwards from 0m/s to 2m/s in 3seconds

the accelerations would be 2/3=0.667m/s2

and F=ma so 240 times 0.667 gives something like 160N

Does this force would have to be an additional force applied to the cables??

so that the total force upwards is 240g+160N ??
 
  • #4
sozener1 said:
so if you want to accelerate the mass upwards from 0m/s to 2m/s in 3seconds

the accelerations would be 2/3=0.667m/s2

and F=ma so 240 times 0.667 gives something like 160N

Does this force would have to be an additional force applied to the cables??

so that the total force upwards is 240g+160N ??

It really pays to keep track of the laws of motion. What tinytim replied is true because of the first law: when the net force on a body is zero, its motion will not change (i.e., it will not accelerate).

Your last question is really a matter of the second law: when there is a net force, the body accelerates in the direction of the net force. You showed that the net force is 160 N, which means
downward force + upward force = 160 N

(Remember to choose one direction as positive and one as negative).
 
  • #5



To determine if the 240kg mass is being lifted up, we would need to consider the forces acting on the object. In this case, we have two cables pulling upwards with a force of 120g each, which would result in a net upward force of 240g. This means that the object is being lifted up, as the net force is in the upward direction. Additionally, we would also need to consider the weight of the object, which is a downward force of 240g due to gravity. However, since the cables are exerting a greater force than the weight of the object, the net force is still in the upward direction and the object is being lifted.

Furthermore, it is important to note that the calculation of force required for lifting may vary depending on the specific situation and factors such as the angle of the cables, the strength and tension of the cables, and any other external forces acting on the object. It is always important to carefully consider all forces and factors when determining the force required for lifting an object.
 

1. How do you calculate the force required for lifting an object?

The force required for lifting an object can be calculated using the formula F = m x g, where F is the force in Newtons, m is the mass of the object in kilograms, and g is the acceleration due to gravity, which is approximately 9.8 m/s^2 on Earth.

2. What is the difference between mass and weight?

Mass is a measure of the amount of matter in an object, while weight is a measure of the gravitational force acting on an object. Mass is constant, but weight can vary depending on the strength of the gravitational field.

3. How does the angle of lift affect the force required?

The angle of lift can affect the force required to lift an object because it changes the direction of the force needed. For example, if you are lifting an object straight up, the force required will be equal to the weight of the object. However, if you are lifting an object at an angle, the force required will be greater because you are also working against the force of gravity pulling the object downwards at an angle.

4. Why is it important to calculate the force required for lifting?

Calculating the force required for lifting is important for safety reasons. If the force required is too great, it could result in injury to the person doing the lifting. It is also important for planning and logistics, as it can help determine the appropriate equipment and techniques needed for lifting a particular object.

5. Is there a maximum weight that a person can safely lift?

Yes, there is a maximum weight that a person can safely lift, and it varies depending on the individual's strength and physical condition. Generally, it is recommended that a person not lift more than 50 pounds (22.7 kilograms) without assistance. It is important to use proper lifting techniques and equipment to avoid injury.

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