Work and energy for a lowered block

In summary: Since the block is accelerating downward, there must be a net force acting downward. Is the tension in the cord upward or downward?In summary, a block of mass 35 kg is being lowered vertically with a constant downward acceleration of g/5. The work done by the cord's force on the block is 2675.4 J. The weight of the block does not contribute to the work done. The kinetic energy of the block is unknown and the speed is also unknown. The equation used to calculate the work done is W = F*d, where F is equal to the sum of the mass times acceleration due to gravity and the mass times acceleration. The force due to the cord is equal to the mass times acceleration plus the
  • #1
Kpgabriel
36
0

Homework Statement


A cord is used to vertically lower an initially stationary block of mass M = 35 kg at a constant downward acceleration of g/5. When the block has fallen a distance d = 6.5 m, find the work done by the cord's force on the block.
Find the work done by the weight of the block.
Find the kinetic energy of the block.
Find the speed of the block.

Homework Equations


W = F*d
F = m*a

The Attempt at a Solution


So I tried finding the first part of the question where I multiplied the mass, 35 kg, and multiplied it by the acceleration, 9.80/5= 1.96, to get F= 198N and then I multiplied the force by the distance to get the work and got 445.9 J but it is wrong.
 
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  • #2
Note: Thread title changed to describe the question subject matter.

Have you drawn a the free body diagram for the situation? What forces are operating on the block? Is the force due to the cord the same as the net force on the block?
 
  • #3
gneill said:
Note: Thread title changed to describe the question subject matter.

Have you drawn a the free body diagram for the situation? What forces are operating on the block? Is the force due to the cord the same as the net force on the block?
No, I do not think it is. So I drew out the free body diagram and I got that the Tension force of the cord, T - mg = ma. So T = ma + mg
For this I got 411.5 N
To solve for work I multiplied it by 6.5m and got 2675.4J which is wrong. I am not sure what I am doing.
 
  • #4
Your equation describes a mass accelerating upwards with acceleration a. Your free body diagram should help you to sort out the directions of the vectors and the signs of the terms in your equation.
 
  • #5
gneill said:
Your equation describes a mass accelerating upwards with acceleration a. Your free body diagram should help you to sort out the directions of the vectors and the signs of the terms in your equation.
So the Tension force would be equal to T= M*g - M*a and that is equal to 274.4N
 
  • #6
That looks reasonable. Be sure to keep track of the directions of the forces acting versus the direction of the motion of the block.
 

FAQ: Work and energy for a lowered block

1. What is work and energy for a lowered block?

Work and energy for a lowered block refers to the amount of force required to move a block from a higher position to a lower position, and the resulting change in energy of the block. This can be calculated using the formula W = F x d, where W is work, F is force, and d is distance.

2. How is work and energy related to a lowered block?

Work and energy are directly related to a lowered block, as work is the amount of energy required to move the block from a higher position to a lower position. The force applied to the block is what causes the change in energy, and the distance it is moved determines the amount of work done.

3. What factors affect work and energy for a lowered block?

The amount of work and energy required to lower a block can be affected by factors such as the weight of the block, the distance it is lowered, and the force applied. The surface the block is being lowered on can also play a role, as friction can impact the amount of force needed to move the block.

4. How can work and energy be calculated for a lowered block?

Work and energy for a lowered block can be calculated using the formula W = F x d, where W is work, F is force, and d is distance. The force applied can be determined by multiplying the mass of the block by the acceleration due to gravity (9.8 m/s^2), and the distance can be measured in meters.

5. Why is understanding work and energy for a lowered block important?

Understanding work and energy for a lowered block is important because it allows us to accurately calculate the amount of force needed to move an object from a higher position to a lower position. This information can be useful in many real-world situations, such as moving heavy objects or designing machines that require lifting or lowering objects.

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