Rotational Kinetic Energy and Angular Momentum

What is the kinetic energy of a 3 kg solid disk (I = 1/2mr2) with a diameter of 80 cm rolling at 4 m/s?

• 12 J

• 24 J

• 36 J

• 48 J

Tags

NGSS.HS-PS3-1

You roll a solid sphere of mass m and radius r (I = 2/5mr2) down a ramp from a height of h, if it starts at rest what is its linear speed at the bottom?

• √1.4gh)

• √2gh)

• √3.5gh)

• √5gh)

A certain star, of mass m and radius r, is rotating with rotational velocity ω. After the star collapses, it has the same mass but with a much smaller radius. Which statement below is true?

• The star’s moment of inertia I has decreased, and its angular momentum L has increased

• The star’s moment of inertia I has decreased, and its angular velocity ω has decreased

• The star’s angular momentum L remains constant, and its rotational kinetic energy has decreased

• The star’s angular momentum L remains constant, and its rotational kinetic energy has increase

An ice skater pulls in her arms at the end of a spinning move.

What does this accomplish?

• She increases her torque which increases her angular speed

• She decreases her rotational energy which increases her angular speed

• She increases her angular momentum which increases her angular speed

• She decreases her inertia which increases her angular speed

Two objects are released from rest at the top of ramps with the same dimensions, as shown in the figure above. The sphere rolls down one ramp without slipping. The small block slides down the other ramp without friction. Which object reaches the bottom of it’s ramp first, and why?

• The sphere, because it gains rotational kinetic energy, but the block does not

• The sphere, because it gains mechanical energy due to the torque exerted on it, but the block does not

• The block, because it does not lose mechanical energy due to friction, but the sphere does

• The block, because it does not gain rotational kinetic energy, but the sphere does.

Tags

NGSS.HS-PS2-1

NGSS.HS-PS2-4