# Kinetic Energy in a pulley system

• scratchfish
Oh, I see now. So the answer is simply 402.5 ft-lb + 201.25 ft-lb + 1207.5 ft-lb = 1811.25 ft-lb. In summary, the kinetic energy of the system of bodies B1, B2 and B3 at an instant when the speed of B1 is 5ft/sec is 1811.25 ft-lb. The units of energy are measured in ft-lb, which is a unit of torque.
scratchfish

## Homework Statement

http://s2.webstarts.com/exploring-my-thought/index.html

Find the kinetic energy of the system of bodies B1, B2 and B3 at an instant when the speed of B1 is 5ft/sec (the image is linked above)

mass of B1 = 32.2lb
mass of B2 = 32.2lb
mass of B3 = 96.6lb

## Homework Equations

translational kinetic energy: K = 1/2mv2
rotational kinetic energy: K = 1/2Iw2

## The Attempt at a Solution

B1 = 1/2(32.2)(5)^2 = 402.5 ft-lb
B2 = 1/2((mr^2)/2)(5/2) = 201.25 ft-lb
B3 = 1/2(96.6)(5)^2 = 1207.5 ft-lb

My answers are way off, what am I doing wrong?

Last edited by a moderator:
How can energy be measured in ft-lb? That doesn't make sense unit wise.

A ft-lb is a unit of torque...

Matterwave said:
How can energy be measured in ft-lb? That doesn't make sense unit wise.

A ft-lb is a unit of torque...

Work = force * distance right?

force unit:lb
distance unit :ft

## 1. What is kinetic energy in a pulley system?

Kinetic energy in a pulley system is the energy that an object possesses due to its motion as it is lifted or lowered by a pulley. It is the energy that is required to overcome the force of gravity and move the object against the resistance of the pulley system.

## 2. How is kinetic energy calculated in a pulley system?

Kinetic energy in a pulley system is calculated using the formula KE = 1/2 * m * v^2, where m is the mass of the object being lifted or lowered and v is the velocity of the object. The velocity can be calculated by dividing the distance the object moves by the time it takes to move that distance.

## 3. How does the number of pulleys in a system affect kinetic energy?

The number of pulleys in a system does not directly affect kinetic energy. However, the use of multiple pulleys can decrease the amount of work needed to lift an object, making it easier to overcome the force of gravity and increase the kinetic energy of the object.

## 4. What factors can affect the amount of kinetic energy in a pulley system?

The amount of kinetic energy in a pulley system can be affected by factors such as the mass of the object, the velocity at which it is being lifted or lowered, the efficiency of the pulleys, and the amount of friction in the system.

## 5. How is kinetic energy in a pulley system useful?

Kinetic energy in a pulley system is useful because it allows for the lifting and lowering of heavy objects with less effort. It is also a key component in various machines and mechanisms, making it possible to perform tasks that would otherwise be impossible without the use of pulleys.

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