Practice Test 1 - High School Physics

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

A 1200 kg car traveling at $v=25\,\text{m/s}$ hits a rigid barrier and must absorb all its kinetic energy through front-end deformation. Three crumple-zone designs are possible, but the available front-end space limits deformation to at most $0.70\,\text{m}$ . Assume the average stopping force can be estimated by $F_{\text{avg}}\approx \text{KE}/d$ . - Design A: deformation distance $d=0.30\,\text{m}$ - Design B: deformation distance $d=0.60\,\text{m}$ - Design C: deformation distance $d=1.00\,\text{m}$ Which design should be selected to minimize average stopping force while still meeting the space constraint?
An electric motor takes in electrical power $P_{in}=500\,\text{W}$ and delivers useful mechanical power $P_{out}=400\,\text{W}$ to lift a load. The rest is lost mainly as thermal energy in the motor. What is the motor's efficiency (as a percentage)?
A metal surface is illuminated with ultraviolet light and emits electrons; the same surface illuminated with bright red light emits none. Which conclusion is best supported by this evidence?
A beaker of warm water is cooled by blowing air across its surface with a small fan. The water cools faster with the fan on than with still air. Which mechanism is most directly increased by turning on the fan?
A compressed spring between two carts on a frictionless 1D track is released. The spring initially stores $16\,\text{J}$ and both carts start at rest. After release, cart A has $12\,\text{J}$ of kinetic energy and cart B has $4\,\text{J}$ . Which statement best describes energy conservation and transfer in this interaction?
A seismology demonstration uses a slinky to model seismic waves. Trial 1 produces a wave with amplitude $A_1$ . Trial 2 produces a wave with amplitude $A_2 = 0.2A_1$ . Assuming the wave energy is proportional to amplitude squared, $E \propto A^2$ , what is the energy ratio $E_2/E_1$ ?
A $6\,\text{kg}$ crate starts from rest at the top of a $12\,\text{m}$ high platform (use $g=10\,\text{m/s}^2$ ). It slides down a frictionless track to the bottom, then moves across a rough horizontal floor for $8\,\text{m}$ where the kinetic friction force is constant at $30\,\text{N}$ , and then goes up a frictionless ramp to a final point where it comes to rest. What maximum vertical height above the floor does the crate reach on the ramp? (Track energy: initial $PE_g \to$ bottom $KE \to$ thermal loss on floor $\to$ final $PE_g$ .)
A $65\,\text{kg}$ passenger experiences a relative speed of $v=14\,\text{m/s}$ in a crash. The airbag/seatbelt system must keep average force $\le 2200\,\text{N}$ by ensuring a long enough stopping time. The current design provides $\Delta t=0.30\,\text{s}$ . Using $F_{\text{avg}}\approx \dfrac{mv}{\Delta t}$ , does the current design meet the force requirement, and if not, what minimum $\Delta t$ is required?
Two point charges lie on the x-axis: $Q_1=+3.0\,\mu\text{C}$ at $x=-0.20\,\text{m}$ and $Q_2=-3.0\,\mu\text{C}$ at $x=+0.20\,\text{m}$ . At the midpoint (the origin), what is the direction of the net electric field $\vec E_{\text{net}}$ ?
A current-carrying wire is placed perpendicular to a uniform magnetic field so that $\theta=90^\circ$ in $F=BIL\sin\theta$ . If the current is increased from $0.5\,\text{A}$ to $1.5\,\text{A}$ while $B$ and $L$ stay the same, what happens to the magnitude of the magnetic force on the wire?
A student heats one end of a rod and compares two materials with the same shape: a copper rod and a plastic rod. The far end of the copper rod becomes hot much sooner than the far end of the plastic rod. This strong dependence on the material (metal vs insulator) is most characteristic of which mechanism?
A student measures ocean surface water waves and finds the distance between consecutive crests is $\lambda = 8.0\ \text{m}$ . If $0.50\ \text{waves/s}$ pass a fixed point (frequency $f = 0.50\ \text{Hz}$ ), what is the wave speed $v$ ? Use $v = f\lambda$ .
A detector measures light coming from a dim source and records discrete "clicks," each corresponding to a single localized detection event. However, when the light passes through a diffraction grating, the clicks accumulate into bright and dark diffraction maxima and minima at specific angles. Which statement best summarizes why wave-particle duality is needed here?
An electric motor operates at an efficiency of $\eta=75\%$ . If it receives $P_{in}=240\ \text{W}$ of electrical power, what useful mechanical power $P_{out}$ does it deliver? Use: $P_{out}=\eta\,P_{in}$ with $\eta$ as a decimal.
Two small charged spheres are treated as point charges. Sphere A has charge $q_1 = +4.0\,\mu\text{C}$ and sphere B has charge $q_2 = +2.0\,\mu\text{C}$ . Their centers are separated by $r = 0.30\,\text{m}$ . Using Coulomb's Law with $k = 9.0\times10^9\,\text{N}\cdot\text{m}^2/\text{C}^2$ , what is the magnitude of the electric force between the spheres (in N)?
A proton ( $m_p = 1.67 \times 10^{-27}\ \text{kg}$ , $q_p = +1.6 \times 10^{-19}\ \text{C}$ ) and an electron ( $m_e = 9.11 \times 10^{-31}\ \text{kg}$ , $q_e = -1.6 \times 10^{-19}\ \text{C}$ ) are separated by $r = 5.3 \times 10^{-11}\ \text{m}$ (Bohr radius). Using $F_{\text{grav}} = G\frac{m_1 m_2}{r^2}$ with $G = 6.67 \times 10^{-11}$ and $F_{\text{elec}} = k\frac{q_1 q_2}{r^2}$ with $k = 9.0 \times 10^9$ , by what factor is the electric force larger than the gravitational force (i.e., compute $F_{\text{elec}}/F_{\text{grav}}$ in magnitude)?
On a low-friction track, Cart A (mass $2.0\,\text{kg}$ ) moves rightward at $v_{A i} = +4.0\,\text{m/s}$ . Cart B (mass $1.0\,\text{kg}$ ) moves leftward at $v_{B i} = -2.0\,\text{m/s}$ . After an inelastic collision (they do not stick), the measured final velocities are $v_{A f} = +1.0\,\text{m/s}$ and $v_{B f} = +4.0\,\text{m/s}$ . Which statement correctly verifies whether momentum is conserved (take rightward as positive)?
Two blocks are in contact on a frictionless surface. Block 1 is pushed to the right (→) and presses on Block 2, causing both to accelerate rightward. Considering only the Block 1–Block 2 contact interaction, which pair of forces is an action-reaction pair?
A laser is aimed at a double-slit apparatus, producing alternating bright and dark fringes on a screen. If the slits are narrowed, the pattern spreads out more. Which model of light best explains the bright/dark fringe pattern and its spreading, and why?
Based on the data shown, a block is on a $30^\circ$ incline and is pulled up the slope at constant speed by a rope. The tension $F_T$ acts up the slope and kinetic friction $F_f$ acts down the slope. In Trial 2, what is the magnitude of the downslope component of weight, $F_{g,\parallel}$ , on the block? (Assume net force along the slope is zero.)

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