What torque must be applied to this flywheel?

In summary, the problem is to determine the torque needed to start a chainsaw by pulling a rope attached to a solid steel flywheel. The flywheel has a mass of 1.5 kg distributed along the outside edge and a diameter of 10 cm. It must accelerate to 4.0 rev/s in 2.0 seconds. To solve this, the equation Angular Acceleration = Torque/Moment of Inertia is used. To convert rev/s to rad/s, the ratio (1 rev)/(2pir) is used. The final answer for the torque needed is 4.7x10^-2 Nm.
  • #1
dancer_smiley
6
0
Here is the problem: A chainsaw is started by pulling on a rope that is attached to a solid steel flywheel. Assume that the wheel has a mass of 1.5 kg that is completely distributed along the outside edge, and it has a diameter of 10 cm. It starts at rest and must accelerate to 4.0 rev/s in 2.0 seconds in order to start the motor. What torque must be applied to the flywheel?

Equation I used: Angular Acceleration = Torque/Moment of Inertia

Here is my attempt: (1.5 kg)(.05 m)^2 (4.0 rev/s / 2.0 s) = .0075

I don't think this is the correct answer, but I have no idea how to solve this question...
 
Physics news on Phys.org
  • #2
You need to convert rev/s to rad/s for this to work.
 
  • #3
Do I divide my answer by 2(pi)rad to do that?
 
  • #4
1 revolution = 2pir

You can use the ratio (1 rev)/(2pir) or (2pir)/( 1 rev) to convert from revolutions to radians or vice versa. You have revs and you want to convert to radians so multiply through the ratio that will cancel out the revs.
 
  • #5
thepatient said:
1 revolution = 2pir

You can use the ratio (1 rev)/(2pir) or (2pir)/( 1 rev) to convert from revolutions to radians or vice versa. You have revs and you want to convert to radians so multiply through the ratio that will cancel out the revs.
One revolution is not 2πr. One revolution is 2π radians without the "r". Then one rev/s is 2π rad/s and x revolutions per second is x*2π rad/s.
 
  • #6
kuruman said:
One revolution is not 2πr. One revolution is 2π radians without the "r". Then one rev/s is 2π rad/s and x revolutions per second is x*2π rad/s.


Yes. XD 2pi = 1 rev. I don't know what I was thinking.
 
  • #7
I multiplied .0075*(2pi)
So that makes my answer .047123?
Is that the correct answer for the problem?
 
  • #8
What units do I use? Is it meters?
 
  • #9
The units of torque are Newton-meters.
 
  • #10
So my answer is 4.7x10^-2 Nm? Is this correct?
 
  • #11
dancer_smiley said:
So my answer is 4.7x10^-2 Nm? Is this correct?
The method is correct and the answer should be if you plugged in the numbers correctly.
 
  • #12
Thank you so much for your help! :)
 

1. What is torque?

Torque is a measure of the rotational force applied on an object. It is typically measured in units of Newton-meters (Nm).

2. How is torque calculated?

Torque is calculated by multiplying the force applied on an object by the distance from the fulcrum point or axis of rotation.

3. What factors affect the torque required for a flywheel?

The factors that affect the torque required for a flywheel include the weight and radius of the flywheel, the speed and direction of rotation, and the amount of friction present.

4. How do I determine the torque needed for a specific flywheel?

To determine the torque needed for a specific flywheel, you will need to know the weight and radius of the flywheel, as well as the desired speed and direction of rotation. Additionally, you will need to consider any external factors such as friction that may affect the torque requirements.

5. What are some common methods for applying torque to a flywheel?

Some common methods for applying torque to a flywheel include using a torque wrench, using a motor or engine, or using a pulley system with a weight attached.

Similar threads

  • Introductory Physics Homework Help
Replies
5
Views
3K
  • Introductory Physics Homework Help
Replies
3
Views
2K
Replies
8
Views
2K
  • Introductory Physics Homework Help
Replies
5
Views
1K
  • Introductory Physics Homework Help
Replies
7
Views
2K
  • Introductory Physics Homework Help
2
Replies
44
Views
3K
  • Mechanical Engineering
Replies
19
Views
2K
  • Introductory Physics Homework Help
Replies
2
Views
2K
  • Mechanical Engineering
Replies
3
Views
2K
  • Introductory Physics Homework Help
Replies
2
Views
844
Back
Top