Here are 100 multiple choice physics questions with answers and rationales: What is the value of the gravitational constant (G) in SI units? A) 6.67 x 10^-11 N⋅m^2/kg^2 B) 9.81 m/s^2 C) 3.00 x 10^8 m/s D) 8.85 x 10^-12 C^2/N⋅m^2 The correct answer is: A Rationale: The gravitational constant G relates the gravitational force between two masses to their masses and separation distance. Its value in SI units is 6.67 x 10^-11 N⋅m^2/kg^2. In the kinetic theory of gases, what particle property causes the pressure exerted by a gas? A) Gravity of the gas particles B) Electrical charge of the gas particles C) Random thermal motion of the gas particles D) Density of the gas particles The correct answer is: C Rationale: According to the kinetic theory, the random thermal motions of gas particles result in collisions with the walls of a container, transferring momentum and causing the pressure exerted by the gas. A 5 kg object is released from rest at a height of 20 m. What is its kinetic energy just before hitting the ground? A) 490 J B) 98 J C) 981 J D) 19.6 J The correct answer is: A Rationale: The initial potential energy is mgh = 5 kg * 9.8 m/s^2 * 20 m = 980 J. With no non-conservative forces, this is converted entirely to kinetic energy 1/2mv^2 just before hitting the ground, which is 490 J. Two point charges exert an electrostatic force of 2 N on each other. If the charges are tripled while their separation doubles, what is the new force between them? A) 6 N B) 18 N C) 1 N D) 0.5 N The correct answer is: B Rationale: The electrostatic force is proportional to the product of the charges and inversely proportional to the square of the separation distance. Tripling the charges increases the force by 3, while doubling the separation decreases the force by 1/4, resulting in a net force of 322 = 18 N. A spacecraft of mass 1000 kg undergoes a constant acceleration of 5 m/s^2 for 10 seconds. What is the change in its kinetic energy during this time? A) 125,000 J B) 250,000 J C) 500,000 J D) 1,000,000 J The correct answer is: A Rationale: The kinetic energy of an object is 1/2mv^2. With constant acceleration a over time t, the final velocity is v = at = 5 m/s^2 * 10 s = 50 m/s. The change in kinetic energy is then 1/21000kg(50 m/s)^2 = 125,000 J. In the Bohr model of the hydrogen atom, what determines the possible energy levels an electron can occupy? A) The principal quantum number B) The spin quantum number C) The orbital quantum number D) The magnetic quantum number The correct answer is: A Rationale: In the Bohr model, the possible electron energy levels are determined solely by the principal quantum number n, with higher n corresponding to higher energy levels. A 2 kg object is whirled in a horizontal circle on a 1 m long massless string. If the string makes an angle of 30° with the vertical, what is the tension in the string? A) 19.6 N B) 29.4 N C) 39.2 N D) 49.0 N The correct answer is: B Rationale: The forces on the object are the tension T and the gravitational force mg. For circular motion, the net force is mv^2/r directed inward. Setting this equal to Tcos(30°) - mgsin(30°) gives T = (2kg*9.8m/s^2)/cos(30°) = 29.4 N. According to the special theory of relativity, what happens to the mass of an object as its speed approaches the speed of light? A) Its mass remains constant B) Its mass decreases C) Its mass increases without bound D) Its mass oscillates periodically The correct answer is: C Rationale: According to Einstein's theory of special relativity, as an object's speed approaches the speed of light, its mass increases towards infinity due to the effects of relativity. A charged particle enters a region with a uniform magnetic field. If the particle's velocity is perpendicular to the magnetic field, what will be its motion? A) A straight line along its initial direction B) A circular path in the plane perpendicular to the field C) A helical path around the direction of the field D) No motion, since the magnetic force is perpendicular to the velocity The correct answer is: B Rationale: For a velocity perpendicular to a magnetic field, the magnetic force qvBsin(90°) = qvB is always perpendicular to v, resulting in a circular orbit with centripetal acceleration provided by this force. Two radio antennas are separated by 500 m and tuned to a frequency of 105 MHz. What is the path difference between the direct ray and a ray reflecting off the ground if the antennas are 30 m high? A) 3 m B) 6 m C) 9 m D) 12 m The correct answer is: B Rationale: The path difference is twice the difference between the direct path and reflected path. Using the Pythagorean theorem, this is 2*sqrt((500 m)^2 + (30 m)^2) - 500 m = 6 m. A thin converging lens has a focal length of 10 cm. An object is placed 15 cm from the lens. Where is the image formed? A) 30 cm from the lens on the same side as the object B) 30 cm from the lens on the opposite side of the object C) 6 cm from the lens on the same side as the object D) 6 cm from the lens on the opposite side of the object The correct answer is: D Rationale: For a thin lens, the object distance p, image distance q, and focal length f are related by 1/p + 1/q = 1/f. Substituting the given values gives q = 6 cm on the opposite side. In the photoelectric effect, how does increasing the intensity of the incident light affect the maximum kinetic energy of the emitted electrons? A) It increases the maximum kinetic energy B) It decreases the maximum kinetic energy C) It has no effect on the maximum kinetic energy D) The effect depends on the frequency of the light The correct answer is: C Rationale: The maximum kinetic energy of photoelectrons depends only on the frequency of the incident light, not its intensity. Higher intensity increases the number of electrons emitted, not their kinetic energies. In Rutherford's gold foil experiment, what did the unexpected deflections of some alpha particles reveal about the atom? A) Atoms have a diffuse, uniform distribution of positive charge B) Atoms have a dense, positive nucleus surrounded by empty space C) Atoms contain quantized negative charge carriers called electrons D) Atoms are mostly empty space with positive and negative charges The correct answer is: B Rationale: Rutherford interpreted the large deflections of some alpha particles as evidence that atoms contain a small, dense, positively-charged nucleus, unlike the expected diffuse distribution of charge. A parallel plate capacitor has a capacitance of 5 microfarads and is charged to 100 V. How much electrostatic energy is stored in the capacitor? A) 2.5 x 10^-4 J B) 2.5 x 10^-3 J C) 2.5 J D) 25 J The correct answer is: C Rationale: The electrostatic energy stored in a capacitor of capacitance C charged to a voltage V is (1/2)CV^2 = (1/2)510^-6