Physics Questions and Answers

Answer: D

RADAR is used for detecting and locating objects such as aircraft.

A pulse of radio waves is transmitted and the echo timed, giving the range as \(d = ct/2\); the antenna's direction gives the bearing, and the Doppler shift gives the speed. Radio waves do not travel through sea water, so submerged submarines are found by sonar.

Answer: B

Pressure is the scalar.

Although it arises from force, pressure at a point in a fluid acts equally in all directions and has no direction of its own, so it is specified by a single number. Force, velocity and acceleration are all vectors.

Answer: C

A solar eclipse occurs when the moon comes between the sun and the earth.

The moon's shadow falls on the earth, and only those in the narrow path of the umbra see totality. It can happen only at new moon, and not at every new moon, because the moon's orbit is tilted about 5° to the ecliptic.

Answer: D

Stock value is not a term in physics.

It belongs to finance. Latent heat is the energy absorbed in a change of state, nuclear fusion the joining of light nuclei, and refractive index the ratio \(c/v\) for a medium.

Answer: C

So that the necessary centripetal force is obtained from the horizontal component of the normal reaction.

Banking tilts the reaction inward: \[\tan\theta = \frac{v^2}{rg}\] The rails then do not have to supply the force by pressing sideways on the flanges, which would cause wear and risk derailment.

Answer: D

The maximum and minimum separations are 3.3 km and 0.30 km.

The listeners are at \[d_1 = 300\times5 = 1500\ \mathrm{m},\qquad d_2 = 300\times6 = 1800\ \mathrm{m}\] from the source. They are furthest apart on opposite sides of it, \(1500+1800 = 3300\ \mathrm{m}\), and closest on the same side, \(1800-1500 = 300\ \mathrm{m}\).

Answer: C

The heating is due to both the heating effect of the current and hysteresis loss.

Copper loss is the \(I^2R\) dissipation in the windings; iron loss is hysteresis plus eddy currents in the core. Laminating the core cuts eddy currents, and a soft-iron core with a narrow hysteresis loop cuts the other - but neither can be eliminated.

Answer: B

The water will not rise above the top of the tube, and it does not overflow.

If the tube is shorter than the calculated capillary height, the liquid rises to the top and stops. The radius of curvature of the meniscus adjusts itself so that \(hr\) stays constant, so the meniscus simply becomes flatter and the water stays put.

Answer: A

Because the atmospheric pressure on the hills is lower, so water boils below 100 °C.

A liquid boils when its vapour pressure equals the surrounding pressure. At 2,000 m water boils at about 93 °C, and food cooks more slowly at the lower temperature. A pressure cooker restores the higher boiling point.

Answer: C

Correct answer: The lift and the person fall with the same acceleration, so the floor exerts no reaction

Weight is felt through the normal reaction of the floor, and when both fall together at \(g\) that reaction drops to zero. Gravity continues to act throughout, which is precisely why they are falling.