Practice Test 8 - High School Physics

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

Two carts collide head-on on a frictionless track. Cart A has mass $m_A=1.0\ \text{kg}$ and initial velocity $v_{A i}=+8.0\ \text{m/s}$ (right). Cart B has mass $m_B=3.0\ \text{kg}$ and initial velocity $v_{B i}=-2.0\ \text{m/s}$ (left). The collision is perfectly inelastic (they stick together). Taking rightward as positive, what is the common final velocity $v_f$ ?
A metal spoon is left in a mug of hot tea at 80°C. After 2 minutes, the handle (which is not in the tea) becomes noticeably warm, even though the air around it is still. Which thermal energy transfer mechanism is primarily responsible for heating the spoon handle (hot tea → spoon handle)?
Three blocks are in a line on a frictionless table: Block A touches Block B, and Block B touches Block C. A hand pushes Block A to the right, so A pushes on B, and B pushes on C. In this situation, which pair of forces is an action-reaction pair for the Block B–Block C contact interaction?
A sound wave at fixed frequency has intensity proportional to amplitude squared: $I \propto A^2$ . A microphone measures intensity $I_1$ when the amplitude is $A_1$ . If the measured intensity becomes $I_2 = 9I_1$ , by what factor did the amplitude change?
A student places a copper spoon (initially 20°C) into a mug of hot tea at 80°C. After 30 seconds, the handle of the spoon feels warmer even though it is not in the tea. Which thermal energy transfer mechanism is primarily responsible for the handle warming up through the spoon material?
A positively charged particle with $q=+2.0\times10^{-6}\ \text{C}$ moves $0.50\ \text{m}$ through a uniform electric field $E=4.0\times10^{3}\ \text{N/C}$ . The displacement is directly opposite the direction of the electric field. How much work does the electric field do on the particle?
Two point charges are separated by $r = 0.060\,\text{m}$ . Charge A is $q_1 = -7.0\,\text{nC}$ and charge B is $q_2 = -5.0\,\text{nC}$ . Using $k = 9.0\times10^9\,\text{N}\cdot\text{m}^2/\text{C}^2$ , what is the magnitude of the electric force between them (in N)?
A 0.20 kg hockey puck (Puck A) slides right at $v_{A i} = +10\,\text{m/s}$ and collides head-on with a 0.40 kg puck (Puck B) sliding left at $v_{B i} = -2.0\,\text{m/s}$ on nearly frictionless ice. After an inelastic collision, Puck A rebounds left at $v_{A f} = -4.0\,\text{m/s}$ . Taking rightward as positive, what is Puck B's final velocity $v_{B f}$ (in m/s)?
A $1.5\,\text{kg}$ cart moving at $6.0\,\text{m/s}$ collides with a stationary $1.5\,\text{kg}$ cart on a track. After the collision, the two carts stick together and move as one. During this interaction, which statement best describes the energy transfer and transformation?
A foldable solar charger converts solar radiation → electrical energy for disaster relief. Under clear sky, use $1000\,\text{W/m}^2$ sunlight. You have a budget that allows at most $A=0.30\,\text{m}^2$ of panels, and the panels are $20\%$ efficient. The charger must provide at least $P_{out}=50\,\text{W}$ . Evaluate the design: what power does it produce, and does it meet the requirement? Use $P_{out}=A(1000)\eta$ .
A battery charger uses $E_{in}=900\ \text{J}$ of electrical energy to store $E_{out}=810\ \text{J}$ as chemical energy in a battery. The rest is lost as heat. What is the charger's efficiency (as a percentage)?
A sports pad is being designed to protect a player's forearm from a puck impact. A puck of mass $m=0.17\ \text{kg}$ moving at $v_i=30\ \text{m/s}$ is brought to rest by the pad. The injury criterion is maximum allowable average force $F_{\max}=1000\ \text{N}$ . Design A: thin hard plastic over foam, stopping time $\Delta t=0.004\ \text{s}$ Design B: thicker foam, $\Delta t=0.010\ \text{s}$ Design C: air-pocket pad, $\Delta t=0.020\ \text{s}$ but it is too bulky for rules if thickness exceeds 5 cm; this design is 6 cm thick. Which option should be selected if it must meet the force limit and comply with the thickness rule?
A lab tests transmission over the same 1 km cable. For analog voice, intelligibility becomes poor below about 40 dB SNR. A digital voice link with error correction can still work around 15–20 dB SNR, but fails if SNR gets too low to distinguish 0 from 1 reliably. If the measured SNR is 18 dB, which result is most likely?
A clear pot of water is heated from below on a stove. After a minute, you can see water moving: warmer water near the bottom rises while cooler water near the top sinks, creating circulating currents. Which mechanism best explains the transfer of thermal energy through the water in this observation?
A string wave has energy proportional to the square of its amplitude: $E \propto A^2$ . Which statement correctly describes the amplitude–energy relationship (with frequency unchanged)?
A battery charger takes in $P_{in}=120\ \text{W}$ from the wall and stores useful chemical energy in the battery at a rate of $P_{out}=102\ \text{W}$ . What is the efficiency $\eta$ (in %)?
A packaging engineer must protect a 2.0 kg camera shipped in a box that may be dropped from 1.2 m. The camera can tolerate a maximum average stopping force of 300 N. Assume the camera's impact speed is $v = \sqrt{2gh}$ with $g = 9.8\ \text{m/s}^2$ , and the packaging brings it to rest over a compression distance $d$ with approximately constant average force. Using work-energy ( $\tfrac12 mv^2 = F_{\text{avg}} d$ ), what minimum compression distance $d$ is required? What is the minimum $d$ ?
A beaker of warm water is left to cool in two trials: Trial 1: The water is left undisturbed. Trial 2: The water is gently stirred continuously. The water cools faster in Trial 2. Which mechanism is most directly increased by stirring, causing the faster cooling?
A heat engine must meet a minimum efficiency requirement of at least $30\%$ . It takes in $E_{in}=8000\ \text{J}$ of thermal energy from fuel and produces $E_{out}=2400\ \text{J}$ of useful work. Does it meet the requirement?
A proton enters a region of uniform magnetic field $\vec{B}$ directed into the page ( $\otimes$ ) with an initial velocity $\vec{v}$ upward. Neglecting gravity, what path will the proton follow while in the field?

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