Practice Test 11 - High School Physics

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

Start practice test

1. Two carts on a low-friction track collide head-on (rightward positive). Cart A: $m_A = 1.0\,\text{kg}$, $v_{A i} = +5.0\,\text{m/s}$. Cart B: $m_B = 2.0\,\text{kg}$, $v_{B i} = -1.0\,\text{m/s}$. After the collision (inelastic; they do not stick), Cart A has velocity $v_{A f} = -1.0\,\text{m/s}$. Using conservation of momentum, what is Cart B's final velocity $v_{B f}$?
2. A solar panel produces $P_{out}=90\ \text{W}$ of electrical power from $P_{in}=600\ \text{W}$ of incoming solar power. What percentage of the input power is lost as waste (mostly thermal)? Use: $P_{lost}=P_{in}-P_{out}$ and $\%\text{ lost}=\left(\frac{P_{lost}}{P_{in}}\right)\times 100\%$
3. To verify momentum conservation with equal masses, two identical carts ($m_1=m_2$) collide on a low-friction track: cart 1 moves rightward toward cart 2, which is initially at rest. Motion sensors are available, and the collision point must be consistent across trials. Which controlled variable is most important to minimize external forces that could change the system's momentum during the collision?
4. A student places a metal spoon (initially 20°C) into a mug of hot tea at 80°C. After 2 minutes, the spoon handle above the tea feels warm (about 35°C) even though it never touched the tea. Which thermal energy transfer mechanism is primarily responsible for heating the spoon handle from the tea end to the handle end?
5. A $10\,\text{kg}$ sled is pulled to the right (→) by a horizontal rope with tension $F_T=80\,\text{N}$. Kinetic friction is $F_f=30\,\text{N}$ to the left (←). Weight $F_g$ (↓) and normal force $F_N$ (↑) cancel vertically. What is the net force on the sled (magnitude and direction)?
6. A water wave has speed $v = 10\ \text{m/s}$. If the wave speed stays constant but the frequency increases from $0.50\ \text{Hz}$ to $1.0\ \text{Hz}$, what happens to the wavelength?
7. A water wave travels at a constant speed. If the frequency increases from $0.40\ \text{Hz}$ to $0.80\ \text{Hz}$ while the wave speed stays the same, what happens to the wavelength $\lambda$?
8. A water wave moves across a lake. The distance between two consecutive crests (wavelength) is $\lambda = 6.0\ \text{m}$, and waves pass a dock at a rate of $f = 0.50\ \text{Hz}$. Using $v = f\lambda$, what is the wave speed $v$ (in m/s)?
9. A metal rod has one end placed in a flame while the other end is held by a clamp. After a short time, the far end becomes hot even though it is not in the flame. No part of the rod is moving as a whole. Which observation best supports that the heating along the rod is due to conduction rather than convection or radiation?
10. A clean metal surface is illuminated with light. Electrons are emitted only when the light frequency is above a certain threshold, and increasing intensity (at fixed frequency above threshold) increases the number of emitted electrons but not their maximum kinetic energy. Which model best explains these results? ​
11. A loudspeaker produces a sound wave at a fixed frequency. The sound energy transferred to the air is proportional to the square of the wave's amplitude: $E = kA^2$. If the speaker's amplitude increases from $A_1$ to $A_2 = 2A_1$, by what factor does the energy change?
12. A single loop of wire lies flat on a table. A uniform magnetic field points straight upward (perpendicular to the loop). Which action will definitely induce an EMF in the loop?
13. A $1200\,\text{kg}$ car traveling at $24\,\text{m/s}$ brakes to a stop over a distance of $48\,\text{m}$ on level ground. Assume the braking force is constant and is the only horizontal force doing work. Using $W_{\text{net}}=\Delta KE$, what is the magnitude of the braking force (in N)?
14. A student heats one end of a rod by holding it against a hot plate. In Trial 1 the rod is copper; in Trial 2 the rod is plastic. The far end of the copper rod becomes warm much sooner than the far end of the plastic rod, even though both are in the same room air. Which mechanism is being tested most directly by changing the rod material?
15. Two light bulbs convert electrical power into light (useful) and heat (waste). - Incandescent bulb: $P_{in}=100\ \text{W}$, useful light output $P_{out}=5\ \text{W}$. - LED bulb: $P_{in}=20\ \text{W}$, useful light output $P_{out}=8\ \text{W}$. Which bulb is more efficient, and by how many percentage points is it more efficient? (Report the difference in efficiency in percentage points.)
16. A solar panel converts $18\%$ of incoming solar energy into electrical energy. If $E_{in}=2500\ \text{J}$ of solar energy strikes the panel, how much electrical energy is produced, $E_{out}$?
17. A 3.0 kg block is launched by a compressed spring on a horizontal surface. The spring constant is $k=200\ \text{N/m}$ and the spring is compressed $x=0.30\ \text{m}$. Assume no friction and that the block starts from rest. What is the block's speed just as it leaves the spring (when the spring returns to its natural length)?
18. A $20\,\text{kg}$ crate is pushed across a horizontal floor at constant velocity. The coefficient of kinetic friction is $\mu_k=0.30$, and take $g=10\,\text{m/s}^2$. The applied force $F_{\text{app}}$ is horizontal. What is the magnitude of the friction force $F_f$ acting on the crate?
19. A new airbag is intended to reduce chest injury by limiting force and pressure. In a crash, the occupant's forward speed relative to the car is reduced from 10 m/s to 0. Two design tweaks are considered: 1) Increase the time the occupant takes to come to rest by venting the airbag so it deflates over a longer time. 2) Keep the same stopping time but make the airbag larger so it contacts a larger area of the chest. Which option best matches the physics-based safety benefit of each tweak?
20. A backpacking group needs a battery system (chemical $\rightarrow$ electrical) to run a GPS unit that draws $P = 6\,\text{W}$ continuously for $t = 5\,\text{h}$. They are considering a $12\,\text{V}$ battery pack. Assume 100% of the battery's stored electrical energy is usable (ignore losses for this problem). What minimum battery capacity (in amp-hours, Ah) is needed? Use: $E = Pt$, $E = VQ$, and $Q(\text{Ah}) = \dfrac{E(\text{Wh})}{V(\text{V})}$.

Practice tests