How It Works

InstaEDU makes it easy to find a great tutor and connect instantly

  • Connect with the perfect tutor, anytime 24/7

    Never get stuck on homework again. InstaEDU has awesome tutors instantly available around the clock.

  • Work together with the best lesson tools

    Our lesson space lets you use video, audio or text. Upload any assignment and work through it together.

  • Try it free—then lock in a super low rate

    Anyone can try InstaEDU for up to 2 hours for free. After that, rates start at just 40¢/minute.

Physics Questions:

To understand and apply the formula τ=Iα to rigid objects rotating about…

Complete Question Text:

To understand and apply the formula τ=Iα to rigid objects rotating about a fixed axis.
To find the acceleration a of a particle of mass m, we use Newton's second law: F_net=ma , where F_net is the net force acting on the particle.
To find the angular acceleration α of a rigid object rotating about a fixed axis, we can use a similar formula: τnet=Iα, where τnet=∑τ is the net torque acting on the object and I is its moment of inertia.

In this problem, you will practice applying this formula to several situations involving angular acceleration. In all of these situations, two objects of masses m1 and m2 are attached to a seesaw. The seesaw is made of a bar that has length l and is pivoted so that it is free to rotate in the vertical plane without friction. Assume that the pivot is attached tot he center of the bar.
You are to find the angular acceleration of the seesaw when it is set in motion from the horizontal position. In all cases, assume that m1>m2.

Assume that the mass of the swing bar, as shown in the figure, is negligible.
Find the magnitude of the angular acceleration α of the seesaw.
Express your answer in terms of some or all of the quantities m1, m2, l, as well as the acceleration due to gravity g.

In what direction will the seesaw rotate, and what will the sign of the angular acceleration be?

The rotation is in the clockwise direction and the angular acceleration is positive.
The rotation is in the clockwise direction and the angular acceleration is negative.
The rotation is in the counterclockwise direction and the angular acceleration is positive.
The rotation is in the counterclockwise direction and the angular acceleration is negative.

Show more
Asked on Oct. 22, 2013, 4:18 p.m.
Keren G. Tutors Physics + 18 others
Massachusetts Institute of Technology (MIT) 2015 - Course 7- Biology
1
"I have a few years of tutoring experience. In high school I volunteered as part of the peer tutoring program and assisted..."

Q2- First let's answer the second question and figure out the direction of the rotation and the sign of the acceleration:
We know- 1) m1 is greater than m2
2)they're both equal distance from the pivot point
3)the only forces acting on the masses is gravity
So- we know m1 will push the seesaw down more on its side, making the seesaw move in a counterclockwise direction from where we stand.
Also in general for angular acceleration counterclockwise movement is positive while clockwise movement is negative.
Ans2- counterclockwise with a positive angular acceleration

Q1- We can split this up into a few steps
1) find net torque on the seesaw adding up the torque applied by each mass using the eqn torque = mass*acceleration
2) find the eqn for moment of inertia for 2 masses. (I= m1*m2*l^2/(m1+m2))
3) set equal and solve for a

So-
1)Tnet= (m1-m2)*g*l/2
2)Tnet= I= m1*m2*l^2*a/(m1+m2)

Ans2- a= (m1-m2)(m1+m2)*g/(2*m1*m2*l)

The student's feedback

Need more help?

          By sending a message, you agree to our Terms of Service.

          686 Physics tutors are available online to help.

          Browse Tutors

          See how InstaEDU works: