Question on Moment of Inertia/Rotational Inertia

  • #1
i_hate_math
150
2

Homework Statement


In the figure, a wheel of radius 0.42 m is mounted on a frictionless horizontal axle. A massless cord is wrapped around the wheel and attached to a 2.7 kg box that slides on a frictionless surface inclined at angle θ = 28 owith the horizontal. The box accelerates down the surface at 1.9 m/s2. What is the rotational inertia of the wheel about the axle?

Diagram attached

Homework Equations


Torque=Moment of Inertia*angular acceleration
F=ma
a=angular acceleration*radius

The Attempt at a Solution


what i did was combinr the equations and yielded the following
I=(F*r^2)/a=0.47628
I don't see where I did wrong but the solution does not match
 

Attachments

  • image.jpg
    image.jpg
    38.2 KB · Views: 377

Answers and Replies

  • #2
haruspex
Science Advisor
Homework Helper
Insights Author
Gold Member
38,742
8,156
I=(F*r^2)/a
You don't say how you calculate the tension. We cannot tell where you went wrong if you do not post your working.
 
  • #3
i_hate_math
150
2
I just realized what I calculated was Fa instead of tension. But how do i find the tension?? I don't know what to do with the angle ø=28°. pls help
You don't say how you calculate the tension. We cannot tell where you went wrong if you do not post your working.
 
  • #4
haruspex
Science Advisor
Homework Helper
Insights Author
Gold Member
38,742
8,156
I just realized what I calculated was Fa instead of tension. But how do i find the tension?? I don't know what to do with the angle ø=28°. pls help
You should draw free body diagrams for both objects, the wheel and the block. Consider the forces on each, the accelerations of each and the relationships between them. The tension affects both.
 
  • Like
Likes i_hate_math
  • #5
i_hate_math
150
2
You should draw free body diagrams for both objects, the wheel and the block. Consider the forces on each, the accelerations of each and the relationships between them. The tension affects both.
thanks heaps, i see what went wrong now. Guess i shouldve drawn a bid and clear free body diagram at the first place!
 

Suggested for: Question on Moment of Inertia/Rotational Inertia

Replies
13
Views
417
Replies
3
Views
245
Replies
21
Views
372
  • Last Post
Replies
3
Views
426
  • Last Post
Replies
3
Views
484
Replies
5
Views
575
Replies
4
Views
381
  • Last Post
Replies
11
Views
657
Replies
4
Views
453
Top