- #1

Taulant Sholla

- 96

- 5

## Homework Statement

## Homework Equations

work-kinetic energy theorem

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In summary, the conversation discusses the concept of work and kinetic energy in relation to a wheel rising over a curb. It is pointed out that assuming a constant force will result in a final kinetic energy of zero. The use of virtual work and rotational kinetic energy is suggested as a possible alternative method. It is also noted that the calculation of average force must be done over the displacement, not just the horizontal distance. The conversation ends with a clarification of the angle used in the calculations.

- #1

Taulant Sholla

- 96

- 5

work-kinetic energy theorem

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- #2

TSny

Science Advisor

Homework Helper

Gold Member

2023 Award

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Can you figure out how much force is required to get the wheel to

- #3

- 41,959

- 10,132

You write that you have to solve it by the Work-KE theorem. I suspect you have misunderstood the requirement. As TSny writes, you have no guarantee that ##\Delta KE=0##.

You can solve statics problems using virtual work. Maybe that is what you are supposed to be using? But that method considers infinitesimal changes in position, not integrating over a substantial change.

- #4

Taulant Sholla

- 96

- 5

Ah, yes. Thank you. It would take a variable force to result in a final kinetic energy of 0. I know torque equilibrium yields the constant force required to offset the torque produced by gravity. Thank you again.TSny said:_{net}to equal zero when F is constant. Try to see why this can't be true.

Can you figure out how much force is required to get the wheel tostartto rise?

- #5

Taulant Sholla

- 96

- 5

Right. Thank you. I need to find the rotational kinetic energy of the wheel once it rises to the top of the curb.haruspex said:

You write that you have to solve it by the Work-KE theorem. I suspect you have misunderstood the requirement. As TSny writes, you have no guarantee that ##\Delta KE=0##.

You can solve statics problems using virtual work. Maybe that is what you are supposed to be using? But that method considers infinitesimal changes in position, not integrating over a substantial change.

- #6

Hamal_Arietis

- 156

- 15

If you assumed that ##ds=-Rd\theta## I think you will get answer

- #7

Monsterboy

- 303

- 96

Isn't that angle = 30^{o} ?

- #8

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Taulant's error was to calculate a funny kind of average force (averaged over horizontal distance, which is not what is meant by "average force") necessary to provide the PE gain. Instead, the force to be found is the minimum constant force that will get it over the step. The next stage is to find the residual KE that results. That could be done by integration, but it is not necessary.Hamal_Arietis said:

If you assumed that ##ds=-Rd\theta## I think you will get answer

Taulant set θ as the angle to the vertical, the 60Monsterboy said:Isn't that angle = 30^{o}?

Torque is a measure of the force that can cause an object to rotate around an axis. It is calculated by multiplying the force applied by the distance from the axis of rotation.

In the context of a wheel turning about a curb, torque is the force that is applied to the wheel to overcome the resistance of the curb and cause the wheel to rotate. The work done by this torque is the energy transferred to the wheel to make it turn.

The work done by torque is calculated by multiplying the torque by the angle through which the wheel turns. This can be represented by the formula W = τθ, where W is the work done, τ is the torque, and θ is the angle in radians.

The distance from the curb affects the work done by torque in two ways. First, a longer distance from the curb will require a higher torque to overcome the resistance and make the wheel turn. Second, a longer distance will result in a larger angle of rotation, leading to a greater amount of work done.

The unit of measurement for work done by torque is joules (J). This is the same unit used for measuring other forms of work and energy.

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