Physics Questions and Answers

Answer: C

The bomb strikes the ground 3.33 km from A.

Vertically it starts with no downward velocity, so \[t = \sqrt{\frac{2h}{g}} = \sqrt{\frac{2\times1960}{9.8}} = \sqrt{400} = 20\ \mathrm{s}\]

Horizontally it keeps the aircraft's speed, \(600\ \mathrm{km/h} = 166.7\ \mathrm{m\,s^{-1}}\): \[x = 166.7 \times 20 = 3334\ \mathrm{m} \approx 3.33\ \mathrm{km}\]

Answer: B

Channel capacity is measured by its bandwidth.

Bandwidth is the range of frequencies the channel can carry, and by the Shannon-Hartley theorem the maximum data rate is \[C = B\log_2\!\left(1 + \frac{S}{N}\right)\] so capacity rises directly with bandwidth. Baud rate counts signal changes per second, which is a different thing.

Answer: A

True. This is Kepler's first law, the law of orbits.

Each planet moves in an ellipse with the sun at one of the two foci. The orbits of the planets are very nearly circular - the earth's eccentricity is only 0.017 - which is why the departure from a circle went unnoticed until Kepler analysed Tycho Brahe's observations of Mars.

Answer: B

It will reach a particular height and remain floating.

The balloon rises while the buoyant force exceeds its weight. As it climbs, the air thins and the upthrust \(\rho_{air}Vg\) falls, until it just balances the weight; there the balloon settles and floats.

Answer: D

This property is inertia.

Newton's first law states that a body continues in its state of rest or of uniform motion in a straight line unless acted on by an external force. Mass is the measure of inertia: the greater the mass, the harder it is to change the state of motion.

Answer: D

Ignition in a diesel engine is produced by compression.

Air alone is compressed to about a twentieth of its volume, which raises its temperature above 500 °C. Fuel injected into that hot air ignites of itself, so a diesel needs no spark plug - hence the name compression-ignition engine.

Answer: A

The SI unit of pressure is the pascal.

\[1\ \mathrm{Pa} = 1\ \mathrm{N\,m^{-2}}\] It is a small unit - atmospheric pressure is about \(10^{5}\) Pa. The dyne and the newton are units of force, and the joule of energy.

Answer: B

Blotting paper works by capillary action.

It is a mesh of loosely packed cellulose fibres with fine pores between them. Ink wets the fibres, so surface tension draws it into the pores, and the narrower the pore the further it is drawn.

Answer: D

The order is IV, III, I, II - visible light, ultraviolet, X-rays, gamma rays.

Frequency rises as wavelength falls: visible light at \(10^{14}\ \mathrm{Hz}\), ultraviolet \(10^{16}\), X-rays \(10^{18}\) and gamma rays above \(10^{19}\). Since \(E = h\nu\), the energy and the penetrating power rise in the same order.

Answer: B

A magnetic field deflects the beam in a television picture tube.

Deflection coils around the neck of the tube sweep the electron beam across and down the screen. Magnetic deflection allows much wider deflection angles than electrostatic plates for the same tube length, which is why an oscilloscope uses plates but a television uses coils.