Practice Test 5 - High School Physics

20 questions. Answer them in any order, then submit to see your score and every explanation.

Two coils are placed close together. The primary coil is connected to a battery through a switch (DC source), and the secondary coil is connected to a galvanometer (no battery in the secondary). When the switch in the primary circuit is closed, the galvanometer in the secondary briefly deflects; when the switch is left closed, the galvanometer returns to zero. What best explains the brief deflection in the secondary?
A $1.5\,\text{kg}$ cart moving at $6.0\,\text{m/s}$ on a level track collides with and sticks to a stationary $1.5\,\text{kg}$ cart. After the collision, the pair moves together more slowly. During this interaction, what happens to the kinetic energy that is not present as kinetic energy after the carts stick together?
A neutral planet and a neutral star attract each other gravitationally but have (approximately) zero net electric force between them. Which explanation best accounts for why gravity dominates planetary orbits even though the electric force constant $k$ is much larger than $G$ ?
A $m=60\,\text{kg}$ skier hits a safety net at $v=10\,\text{m/s}$ . The net system is designed to increase collision time to reduce average force. Safety requirement: $F_{\max}=1500\,\text{N}$ . Due to installation constraints, the longest achievable stopping time is $\Delta t_{\text{max}}=0.30\,\text{s}$ . What is the minimum stopping time required, and what conclusion follows? (Use $\Delta t_{\min}=\frac{mv}{F_{\max}}$ .)
A rear-end collision occurs on a straight, icy road (treat external forces as negligible during the short collision). Car A has mass $m_A=1000\ \text{kg}$ and is moving at $v_{A i}=+20\ \text{m/s}$ (east). Car B has mass $m_B=1000\ \text{kg}$ and is moving at $v_{B i}=+10\ \text{m/s}$ (east). The cars lock together in a perfectly inelastic collision. Taking east as positive, what is their common final velocity $v_f$ ?
A heat engine must meet a minimum efficiency requirement of 30%. In one test, it takes in $E_{in}=6000\ \text{J}$ of thermal energy and produces $E_{out}=1650\ \text{J}$ of useful mechanical work. Does it meet the requirement?
A 2.0 kg box slides down a rough incline from a vertical height of 10 m and reaches the bottom with speed 8.0 m/s (take $g = 10\ \text{m/s}^2$ ). Which conservation-of-energy equation correctly accounts for the energy transformed to thermal energy due to friction during the slide? (Use $E_{\text{thermal}}$ for the thermal energy gained.)
A school wants to connect two buildings with a $300\,\text{m}$ cable run in an area with occasional interference. They can send an analog intercom signal or a digital voice signal. The key requirement is that the message must be delivered correctly (low error rate), even if it sometimes needs a brief retry. Which option is better suited and why?
To investigate momentum conservation in a 1D collision, your lab has the following available items: dynamics carts on a low-friction track, motion sensors, a video camera with analysis software, a balance/scale, and a meter stick. Which equipment set is most essential to directly verify $p_{before}=p_{after}$ with minimal uncertainty?
Based on the data shown, a $2.0\,\text{kg}$ block is pulled to the right on a level table. The applied force $F_{app}$ is to the right and kinetic friction $F_f$ is to the left. What is the magnitude of the net horizontal force on the block in Trial 4?
You stand 1 meter from a campfire and feel warmth on your face even though you are not touching anything hot. A large sheet of clear glass is placed between you and the fire; you still feel some warmth, but a polished aluminum sheet placed between you and the fire greatly reduces the warmth you feel. Which mechanism is primarily responsible for heating you at a distance (fire \u2192 your face)?
Earth and the Moon attract each other gravitationally. Use $M_E = 6.0 \times 10^{24}\ \text{kg}$ , $M_{\text{Moon}} = 7.3 \times 10^{22}\ \text{kg}$ , center-to-center distance $r = 3.8 \times 10^8\ \text{m}$ , and $G = 6.67 \times 10^{-11}\ \text{N}\cdot\text{m}^2/\text{kg}^2$ . What is the magnitude of the gravitational force between Earth and the Moon?
A student shakes a rope to send a traveling wave. Keeping the frequency the same, they want the wave to carry 9 times as much energy as before. For waves on a rope, $E \propto A^2$ . What must happen to the amplitude?
On a low-friction track, Cart A (mass $m_A = 2.0\ \text{kg}$ ) moves rightward at $v_{A i}=+6.0\ \text{m/s}$ and collides with Cart B (mass $m_B=1.0\ \text{kg}$ ) that is initially at rest ( $v_{B i}=0\ \text{m/s}$ ). The collision is perfectly inelastic (the carts stick together). Taking rightward as positive, what is the common final velocity $v_f$ immediately after the collision?
In a 15 m/s crash test, an airbag is added to reduce chest injury. Which statement best explains why an airbag reduces injury risk using physics principles? Assume the occupant must go from 15 m/s to 0 m/s either way.
A $20\,\text{kg}$ cart speeds up from $3.0\,\text{m/s}$ to $9.0\,\text{m/s}$ on a level track. During this process, what is the change in the cart's kinetic energy $\Delta KE$ (in J)?
Earth pulls on the Moon with a gravitational force magnitude given by $F = G\dfrac{M_E M_{\text{Moon}}}{r^2}$ , where $G = 6.67 \times 10^{-11}\,\text{N}\cdot\text{m}^2/\text{kg}^2$ . In this situation, what is the magnitude of the force that the Moon exerts on Earth?
A $90\,\text{kg}$ test dummy moves at $12\,\text{m/s}$ just before being restrained by a safety harness. You can adjust the harness "give" (stopping time) by changing webbing and load limiter settings. The goal is to minimize average force on the dummy while meeting the requirement $F\le 2500\,\text{N}$ . A design constraint is that the harness system cannot allow a stopping time longer than $0.50\,\text{s}$ (to prevent excessive forward motion). Using $F_{\text{avg}}=\Delta p/\Delta t$ , what is the minimum stopping time required, and does it violate the $0.50\,\text{s}$ constraint?
A student records a guitar onto (1) a vinyl record (analog grooves representing a continuous waveform) and (2) a CD-quality file (digital samples stored as binary). The student then adds background electrical noise during playback. Which observation about the effect of noise is most accurate?
A $20\,\text{kg}$ box rests on a $30^\circ$ incline (angle measured from the horizontal). Assume $g=10\,\text{m/s}^2$ . The forces on the box are: weight $F_g$ straight down (↓), normal force $F_N$ perpendicular to the incline, and static friction parallel to the incline. Based on this situation, what is the magnitude of the normal force $F_N$ on the box?

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