10 questions. Try each one, then open the answer to check yourself and read the explanation.
A stone is thrown vertically upward with a speed of 30m/s. Neglecting air resistance, how long will it stay in the air before returning to the thrower's hand?
Answer: D (6s)
Time to the top: t = u/g = 30/10 = 3 s. Coming down takes the same time, so it is in the air for 3 + 3 = 6 s.
A car of mass 1200kg moves around a circular track of radius 25m at a speed of 10m/s. What is the centripetal force acting on the car?
Answer: C (4800N)
F = mv²/r = 1200 × 10² ÷ 25 = 120000 ÷ 25 = 4800 N.
An object weighs 10N in air and 7N when completely immersed in water. What is the relative density of the object?
Answer: B (3.33)
Relative density = weight in air ÷ loss of weight in water = 10 ÷ (10 − 7) = 10 ÷ 3 = 3.33.
Which of the following is the most effective method of heat transfer through a vacuum?
Answer: A (radiation)
Conduction and convection need particles of a medium. Radiation travels as electromagnetic waves, so it is the only way heat crosses a vacuum.
A convex lens forms a real image twice the size of the object. What is the object distance from the lens in terms of the focal length (f)?
Answer: B (1.5f)
Magnification 2 means v = 2u. Then 1/u + 1/(2u) = 1/f, so 3/(2u) = 1/f and u = 1.5f.
A 12V battery supplies a current of 3A for 2 hours. How much energy is supplied in kJ?
Answer: D (259kJ)
E = VIt = 12 × 3 × (2 × 3600 s) = 259200 J, which is about 259 kJ.
Which of the following will not increase the magnitude of the induced emf in a coil?
Answer: C (slowing down the relative motion)
Induced emf depends on how fast the magnetic flux changes. Slowing the motion makes the flux change more slowly, so the emf falls.
An alternating current has a peak value of 10A. What is its rms value?
Answer: B (7.1A)
I(rms) = I(peak) ÷ √2 = 10 ÷ 1.414 ≈ 7.1 A.
A transformer has 500 turns in the primary coil and 100 in the secondary. If the primary voltage is 220V, what is the secondary voltage?
Answer: A (44V)
Vs/Vp = Ns/Np, so Vs = 220 × 100 ÷ 500 = 44 V (a step-down transformer).
In the photoelectric effect, increasing the intensity of light increases
Answer: B (the number of electrons emitted)
Brighter light means more photons, so more electrons are released. Their energy depends only on the frequency of the light.