Exam 1: Conservation Laws Constrain Interactions

One can raise a quantity $q$ to a power a when a has units

An object has an initial position $\overrightarrow{r_{1}}$ , but is found a short time later at position $\overrightarrow{r_{2}}$ , where $\overrightarrow{r_{1}}=\left[\begin{array}{r}1)5 \mathrm{~m} \\2)0 \mathrm{~m} \\-4)2 \mathrm{~m}\end{array}\right], \overrightarrow{r_{2}}=\left[\begin{array}{r}1)5 \mathrm{~m} \\-3)0 \mathrm{~m} \\-4)2 \mathrm{~m}\end{array}\right]$ In a frame in standard orientation on the earth's surface, what is the direction of the object's displacement during this time interval?

Is the specified change in the following objects' thermal energies due to a flow of heat (A), work (B), or some other flow of energy (E)? -Infrared laser light falling on a metal slab makes it hot.

Consider the displacement vectors shown below. - Which is equal to $-\vec{C}$ ?

An object of mass $m$ traveling at speed $\vec{v}_{0}$ in the $+x$ direction hits an identical object at rest. Characterize each of the collision outcomes shown below as being (A) absurd or (C) credible. (The collisions are not necessarily elastic, but they are not super-elastic.) -

Suppose we use a string to suspend a ball from a hook in the ceiling. As the ball swings back and forth, which interaction does work on the system if -we consider the system to be the ball and the earth?

A system of two noninteracting particles might have a negative total energy $E$ .

Consider the types of reference frames listed below. (NRF = nonrotating frame) -A reference frame attached to a freely falling elevator A. A NRF in deep space B. A NRF that is freely floating C. A NRF attached to the earth's center of mass D. A frame attached to the earth's surface (or a similarly slowly rotating object) E. A frame moving at a constant velocity relative to one of the frame types described above F. A noninertial frame

Initially, the light puck is moving east at $3 \mathrm{~m} / \mathrm{s}$ while the heavy puck is moving west at $2 \mathrm{~m} / \mathrm{s}$ . The final velocity of the conjoined pucks is

To which of the following two-object systems can we apply conservation of momentum, and why? In each case, answer "A" if we can apply conservation of momentum because the system floats in space, "F" if it's because the system is functionally isolated, " $C$ " if it's because the system undergoes a collision, and " $\mathrm{D}$ " if momentum is not conserved at all because the system is not isolated. -Two magnetic hockey pucks slide on a flat plane of frictionless ice. They attract each other as they pass, changing each other's trajectories without touching.

The basic SI units of angular momentum are:

A person is sitting at rest on a stool that is free to rotate about a vertical axis. The person holds a bicycle wheel that is rapidly spinning counterclockwise when viewed from above. The person then flips the wheel over. What happens as a result?

Which of the following things is an "extended object"? For each item, answer "A" if the item is an acceptable extended object, " $\mathrm{B}$ " if the definition of an extended object applies badly to the item, and " $\mathrm{D}$ " if it is debatable. -A rock

Which of the lettered graphs below might also legitimately describe the potential energy for the same interaction (between the same two particles!) whose potential energy function is shown in the "original" graph in the upper left? In each case, the vertical axis is energy (increasing upward) and that axis crosses the horizontal axis where $r=0$ .

Which of the following things is an "extended object"? For each item, answer "A" if the item is an acceptable extended object, " $\mathrm{B}$ " if the definition of an extended object applies badly to the item, and " $\mathrm{D}$ " if it is debatable. -A swarm of bees

Suppose we launch a disk so it rolls without slipping up an incline. The disk of course slows down as it moves up the incline. But in what direction does the friction force acting on the disk point?

Suppose the average thermal speed of molecules in a gas at room temperature $\left(22^{\circ} \mathrm{C}\right)$ is $\left|\vec{v}_{0}\right|$ . If we "double" the gas's temperature (to $44^{\circ} \mathrm{C}$ ), what is the average molecular speed now? Select the closest response.

An object of mass $m$ traveling at speed $\vec{v}_{0}$ in the $+x$ direction hits an identical object at rest. Characterize each of the collision outcomes shown below as being (A) absurd or (C) credible. (The collisions are not necessarily elastic, but they are not super-elastic.) -

If the sound level increases by 20 decibels, by about how much has the intensity of sound (in $\mathrm{W} / \mathrm{m}^{2}$ ) increased?

Consider a collision where an object with a known mass and known speed collides with another object at rest. The objects are free to move in three dimensions. -(b) If the collision is elastic, how many equations of constraint do we have on those quantities?