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Physics 218 Mechanics

Instructor Dr. Tatiana Erukhimova

Lecture 37 Exam from 6 pm to 8 pm

Circular Motion

y

x

Quiz from Nov. 16

The block of mass M is placed on a rotating

platform, a distance L from the center. The

coefficient of friction between the block and the

platform is ?. What is the largest constant

value that ? can have before the block starts

slipping?

Ex.5

A wheel, with radius 0.5 m and moment of inertia

50 kg m2 about its center, rotates about a

frictionless axle with angular velocity 10

radians per second. A brake is applied which

supplies a constant force to a point on the

perimeter of the wheel of 10 N, tangent to the

wheel and opposing the motion. How many

revolutions will the wheel make before coming to

rest?

Ex. 4

A platform can rotate, without friction, about a

vertical axle through its center with a moment of

inertia, Ip. A small bug of mass m is placed on

the platform at a distance b from the center, and

the system is set spinning with angular velocity

?0 (Clockwise as viewed from above). a) What is

the total angular momentum of the system with the

bug at rest on the platform? b) What is the total

angular momentum if he runs in the opposite

direction to the platforms rotation? c) Is it

possible for a little bug to stop the big

platform from rotating?

Pr. 1

A bullet of mass m is fired in the negative x

direction with velocity og magnitude V0, starting

at x x0, yb. (y remains constant) What is its

angular momentum, with respect to the origin, as

a function of x? Neglect gravity.

Conservation of Momentum

If the collision is perfectly elastic, the

kinetic energy is conserved!

Two disks are spinning on a frictionless axle.

The one on the left has mass M, radius RL, and

moment of inertia about the axle IL. It is

spinning with ?L in the direction shown. It is

moving to the right with velocity of magnitude

v0. The one on the right has mass M, radius RR,

and moment of inertia about the axle IR. It is

spinning with ?R in the direction shown. It is

moving to the left with velocity of magnitude v0.

When the two disks collide they stick together.

What is the velocity and the angular velocity of

the combined system after the collision?

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Torque and Angular Momentum

Conservation of Angular Momentum

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Help Session

When tonight at 710 pm

Where

202 James J. Cain Engineering/Physics Lab

Building

Spence St.

Have a great day! Hw Be prepared for the

test Good luck!