Mechanics & Energy
Clue: This quantity is calculated by multiplying force by the perpendicular distance from the axis of rotation.
moment of force
This quantity is calculated by dividing mass by volume.
Density
This equation relates the speed of a wave to its frequency and wavelength.
v=f\lambda ?
A resistor has a potential difference of 12 V across it and a current of 3 A flowing through it. Calculate its resistance.
4 ohms
1. I travel through space and time, sometimes I bounce, sometimes I bend. I can be loud or light, but I never end. What am I?
2. I am born inside but lost outside. I am greater than what you measure at the ends. What am I?
A wave
Electromotive force (e.m.f.)
This quantity is calculated when a force causes displacement, even if the force is not aligned with the motion.
Work
This force equals the weight of fluid displaced by a submerged object.
Upthrust
A string fixed at both ends vibrates in its second harmonic. If the string is 1.2 m long, how many nodes and antinodes are present?
A copper wire of length 2 m and cross-sectional area 1.0 x 10-6 m2 has a resistivity of 1.7 x 10-8 Ohms. Calculate its resistance.
0.034 Ohms
1. I flow without legs, I light without fire. I’m invisible, yet I power your desire. What am I?
2. I am born when two meet, I can be louder or silent. Sometimes I vanish, sometimes I roar. What am I?
Electric Current
Interference of waves (constructive and destructive)
A car of mass 1000 kg increases its speed from 10 m/s to 20 m/s. Calculate the change in kinetic energy.
150,000 Joules
A spring stretches 0.05 m under a 10 N force. Calculate its stiffness constant.
200 N/m
Light travels from glass (n=1.5) into air. Calculate the critical angle for total internal reflection.
41.8 Degrees
A circuit transfers 2400 J of energy when 200 C of charge flows through a component. Calculate the potential difference across the component.
Answer: What is 12 volts?
12V
1. True or False: Astronauts in orbit are weightless because there is no gravity in space. Explain
2. I vanish when you use me, yet I am never gone. I change my clothes, but I never die. What am I?
False - Explanation: Gravity still acts on them; they are in continuous free fall, which creates the sensation of weightlessness.
Energy
A 2 kg ball is dropped from a height of 10 m. Ignoring air resistance, calculate the speed of the ball just before hitting the ground using conservation of energy.
14 m/s
A wire of cross-sectional area 2 x10-6 m2 stretches 1 mm under a 100 N force. Its original length is 2 m. Calculate its Young modulus.
1 x 108 Pa
A metal surface has a work function of phi =2.0 eV. When light of frequency 1.2 x 1015 Hz is incident on it, calculate the maximum kinetic energy of the emitted electrons in electronvolts.
3.0 eV
A cell has an e.m.f. of 1.5 V and internal resistance of 0.4 Ω. When connected to a 5 Ω resistor, calculate the terminal potential difference.
1.36 volts
1. I am everywhere and nowhere, I am both a ripple and a bullet. You cannot see me directly, yet I make your screens glow. What am I?
2. True or False: Increasing the intensity of light always increases the kinetic energy of photoelectrons.
A photon (wave‑particle duality)
False - Explanation: Kinetic energy depends on photon frequency, not intensity. Intensity only increases the number of electrons emitted.
A motor lifts a 50 kg load vertically by 4 m in 10 seconds. The motor consumes 2500 J of electrical energy during this time. Calculate the efficiency of the motor
78.4 %
A small sphere of radius 1.0 x 10-3 m falls steadily through oil at a constant speed of 2.0 x 10-2 m/s. The density of the sphere is 8000 kg/m3 and the density of the oil is 900 kg/m3. Using Stokes’ Law, estimate the viscosity of the oil.
1.2 Pa.s
An electron is accelerated through a potential difference of 150 V. Estimate its de Broglie wavelength.
1.0 x 10-10 m
Explain why the resistance of a negative temperature coefficient thermistor decreases as temperature increases, using the particle model of solids.
Increased temperature causes more lattice vibrations, which release more conduction electrons, reducing resistance.
1. I can stand still yet move, I have nodes and antinodes, and I sing in strings and pipes. What am I?
2. I hold the planets in place, yet I am weaker than a magnet. I bend light, but I cannot be seen. What am I?
A standing wave
Gravity