PHYS 1111 Test #3 Review

A system that has zero momentum must have zero kinetic energy

False

An inelastic collision is characterized by

The total momentum of the system is conserved

For a hoop of mass M and radius R that is rolling without slipping, which is larger, its transnational kinetic energy or its rolling kinetic energy?

They are equal

If the force on an object is zero, the potential energy of the system is zero

False

If the potential energy of the system is zero, the force on the object is zero

False

The potential energy of a system can be negative

True

You drop a ball to the ground from rest and from the same height throw a second identical ball down to the ground. Their changes in gravitational potential energies are the same

True

The change in potential energy has physical meaning, but its value does not

True

A system of particles with zero momentum must also have zero kinetic energy

False

It is possible for two isolated objects to collide so that all the initial kinetic energy of the system is lost

True

Two cars collide at an intersection, but do not "stick together" after the collision. Therefore, the collision is elastic

False

Two cars collide with each other in a horizontal surface, the kinetic energy before and after collision are the same. Therefore, the collision is elastic

True

A system of particles with zero kinetic energy must also have zero momentum

True

An object at rest on a slick surface is struck by a second object. After the collision, both objects must be moving

False

Correlation of I (moment of inertia) and velocity

Larger I = smaller v

Smaller I = larger v

Correlation of I (moment of inertia) and radius

Larger radius = larger I

Smaller radius = smaller I

You drop a ball to the ground from rest, and, from the same height, throw a second identical ball down to the ground. Their change in gravitational potential energies are different

False

Gravitational potential energy value can be positive, negative, and even equal to zero

True

Newton's laws are true for all frames of reference

False

The rotational kinetic energy is a scalar, but the angular momentum is a vector

True

Kinetic friction can do positive work on an object

False

Static friction can do positive work on an object

True

The rotational kinetic energy is a scalar but the angular momentum is a vector

True

An object at rest on a frictionless surface is struck by a second object, after the collision, both objects must be moving

False

Two children ride on a merry-go-round, with child 1 at a greater distance from the axis of rotation than child 2.

i) Is the angular speed of child 1 greater than, less than, or the same as that of child 2?

ii) Is the linear (or tangential) speed of child 1 greater than, less than, or the same as that of child 2?

i) the same as

ii) greater than

In the class demonstration, the instructor sits on a piano stool holding a sizable mass in each hand. Initially, the instructor holds his arms outstretched and spins about the axis of the stool with an angular speed of Wi. While still spinning, the instructor pulls his arm into his chest resulting in an angular speed of Wf.

i) Compare the angular speed:

a. Wf > Wi

b. Wf < Wi

c. Wf = Wi

ii) Reason:

a. moment of inertia increases

b. moment of inertia decreases

c. potential energy changes

i) A

ii) B

Four massive spheres connected by massless rods, each of mass 1 kg, are placed in the position which is 1 m far from the axis of rotation. The moment of inertia of the rotational system is:

a. 1 kg*m

b. 2 kg*m

c. 3 kg*m

d. 4 kg*m

D

The period of the minute and second needle watch are:

a. 3600 sec and 60 sec

b. 60 sec and 3600 sec

c. the same

A

A solid sphere and a hallow sphere of the same mass, m, and radius, R, roll without slipping at the same speed. Is the kinetic energy of the solid sphere more than, less than, or the same as the kinetic energy of the hollow sphere?

Less than

A disk and a hoop of the same mass and radius are released at the same time at the top of an inclined plane. Does the disk reach the bottom of the plane before, after, or at the same time as the hoop?

Before

The rotating systems shown below differ only in that the two spherical movable masses are positioned either far from the axis of rotation (left), or near the axis of rotation (right). If the hanging blocks are released simultaneously from rest, is it observed that

a. the black at left lands first

b. the block at right lands first

c. both blocks land at the same time

B

Does an object moving in a straight line have non-zero angular momentum

a. always

b. sometimes

c. never

B

The rotating systems shown below differ only in that the two spherical movable masses are positioned either far from the axis of rotation (left) or near the axis of rotation (right). Which statement is correct?

a) moments of inertia of the left system is smaller

b) moment of inertia of the right system is smaller

c) moments of inertia of them are the same

B

Consider a tall, skinny pine tree, initially upright, that falls over in a forest. As it is falling, its base remains in contact with the ground and does not move from side to side.

WHAT SORT OF PATH DOES THE TREE'S CENTER OF MASS FOLLOW AS IT FALLS

Circular

Consider a tall, skinny pine tree, initially upright, that falls over in a forest. As it is falling, its base remains in contact with the ground and does not move from side to side.

AS THE TREE FALLS, THE VERTICAL COMPONENT OF THE FORCE EXERTED ON IT BY THE GROUND IS

Less than the tree's weight