Physics Questions and Answers

Answer: A

Angular momentum remains constant.

Gravity acts along the line joining the satellite to the earth's centre, so it exerts no torque about that centre and \(\vec{L} = \vec{r}\times\vec{p}\) is conserved. In a circular orbit the speed is constant too, but the linear velocity is not, since its direction changes continuously.

Answer: A

True. This is Archimedes' principle.

The apparent loss in weight equals the weight of the fluid displaced: \[F_B = \rho_{fluid}V_{displaced}\,g\] It follows from the pressure being greater at the bottom of the immersed body than at the top.

Answer: A

One astronomical unit is the average distance between the earth and the sun.

It is about \(1.496\times10^{11}\) m, or 150 million km, and light covers it in some eight minutes. It is the natural yardstick for distances inside the solar system: Jupiter is 5.2 AU from the sun and Neptune 30.

Answer: D

The maximum speed is 14 m/s.

On an unbanked track the friction supplies the centripetal force: \[\frac{mv^2}{r} \le \mu mg \Rightarrow v_{max} = \sqrt{\mu r g}\]

\[v_{max} = \sqrt{0.2 \times 100 \times 9.8} = \sqrt{196} = 14\ \mathrm{m\,s^{-1}}\]

Answer: D

Temperature cannot be expressed in terms of any of them.

It is one of the seven base quantities of the SI system, alongside length, mass, time, current, amount of substance and luminous intensity. A base quantity is by definition independent of the others and cannot be derived from them.

Answer: A

Newton's first law is the law of inertia.

It states that a body remains at rest or in uniform motion in a straight line unless an external force acts on it, so it defines inertia and identifies the inertial frames in which the other two laws hold.

Answer: A

A solar cell converts solar energy into electrical energy.

Photons above the band-gap energy free electron-hole pairs in a semiconductor, and the built-in field at the p-n junction separates them, driving a current through an external circuit. It is the photovoltaic effect.

Answer: A

At minimum deviation, the angle of emergence equals the angle of incidence.

The ray passes symmetrically through the prism, parallel to its base, so \(i = e\) and \(r_1 = r_2\). That symmetry gives the prism formula \[n = \frac{\sin\left(\frac{A+D_m}{2}\right)}{\sin\left(\frac{A}{2}\right)}\]

Answer: C

Sunlight reaches us in about 8 minutes.

\[t = \frac{d}{c} = \frac{1.5\times10^{11}}{3\times10^{8}} = 500\ \mathrm{s} \approx 8\ \text{minutes 20 seconds}\] So we always see the sun as it was eight minutes ago.

Answer: C

Pure water freezes at 32 °F.

\[F = \frac{9}{5}C + 32 = \frac{9}{5}(0) + 32 = 32\] Fahrenheit set zero at the temperature of a brine mixture, which is why the freezing point of water falls at 32 rather than at 0 on his scale.