Exam 1: Conservation Laws Constrain Interactions

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)? -A drill bit gets hot as it drills a hole in a metal slab.

Suppose we take a disk of radius $R$ and remove the material from $r=0$ to $r=\frac{1}{2} R$ , making a hole at the center of the disk. Note that this decreases the mass of the disk. Will the value of $\alpha$ for the new object be larger, smaller, or the same as that for the original object?

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)? -A bicycle pump becomes hot when operated.

A small person with a surface area of about $1.0 \mathrm{~m}^{2}$ must (by the Stefan-Boltzmann law) radiate energy at a rate that would require eating 11,000 food calories a day if they are naked in a vacuum in deep space. Which do you think is the most important reason that someone sitting in a normal room requires less than 2000 calories a day?

Water slowly evaporates from your skin.

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 the following graph shows the potential energy function for a certain hypothetical interaction. This interaction is

An object of mass $m_{1}$ moving in the $+x$ direction collides with another object at rest with mass $m_{2}$ . After the collision, the object with mass $m_{2}$ is observed moving in the $+y$ direction. Such a collision cannot be elastic, no matter what $m_{1}$ and $m_{2}$ might be.

The set of particles shown below all have the same mass and speed. Which has the largest magnitude of angular momentum around the point $O$ ?

The only way a vector's magnitude can be zero is if all its components are zero

An empty floating boat interacts gravitationally with the earth. A different interaction with something else keeps the boat from responding to the gravitational interaction by sinking. -What is the other object that interacts with the boat?

Consider the solar system as a "system" of particles. Which of the below qualify as internal interactions (A) and which as external interactions (E)? -The gravitational interaction between two planets

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. -(a) How many quantities suffice to completely determine the system's final state (that is, the outgoing objects' velocities and their combined change in internal energy)?

Suppose I push a block along a tabletop at a constant velocity. If I exert a constant forward force of $\vec{F}$ on the block and push it through a distance $D$ , I do work on the block equal to $|F| D$ . Since the block's kinetic energy does not change, friction must be exerting a backward force on the block of the same magnitude as $\vec{F}$ (so that the net force on the block is zero, as required to maintain the block's constant velocity). What work does the friction force do on the block?

As the disk rolls up the incline in the situation described in the previous problem, the friction force acting on the disk does

Suppose a planet with mass $M$ has a moon with mass $M$ . Where is the system's center of mass? Refer to the diagram below.