- #1
Taulant Sholla
- 96
- 5
Homework Statement
Homework Equations
work-kinetic energy theorem
Work done by torque: wheel turning about a curb
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.
work-kinetic energy theorem
- #2
TSny
Science Advisor
Homework Helper
Gold Member
2023 Award
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You've assumed that it is possible for Wnet 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 to start to rise?
Can you figure out how much force is required to get the wheel to start to rise?
- #3
- 41,959
- 10,132
Further to TSny's hints...
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.
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:
- #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:
- #6
Hamal_Arietis
- 156
- 15
You assumed that ##ds=Rd\theta## but ##ds>0## and ##d\theta <0##. So it is wrong
If you assumed that ##ds=-Rd\theta## I think you will get answer
If you assumed that ##ds=-Rd\theta## I think you will get answer
- #7
Monsterboy
- 303
- 96
Isn't that angle = 30o ?
- #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:
Taulant set θ as the angle to the vertical, the 60o. That reduces as the wheel rises.Monsterboy said:
FAQ: Work done by torque: wheel turning about a curb
1. What is torque?
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.
2. How is torque related to work done by a wheel turning about a curb?
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.
3. How is the work done by torque calculated?
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.
4. How does the distance from the curb affect the work done by torque?
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.
5. What is the unit of measurement for work done by torque?
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.