6 questions. Try each one, then open the answer to check yourself and read the explanation.
A palm fruit dropped to the ground from the top of a tree 45m tall. How long does it take to reach the ground?
Answer: D (3s)
From rest, h = ½gt2: 45 = 5t2, so t2 = 9 and t = 3 s (g = 10 m s−2).
The total capacitance of the circuit below is
Answer: B (1.50mF)
The three 2 mF capacitors in parallel give 6 mF. In series with 2 mF: C = (2 × 6)/(2 + 6) = 1.5 mF.
What is the resultant resistance of the circuit in the diagram?
Answer: C (8Ω)
The two 2 Ω resistors in parallel give 1 Ω. Adding 3 Ω and 4 Ω in series: 3 + 1 + 4 = 8 Ω.
In a resonance tube experiment as shown in the diagram, the frequency of the tuning fork is 750Hz and the resonating length of the air column is 0.3m as shown. The velocity of the wave is
Answer: C (300ms−1)
The diagram shows an antinode at the top, a node, an antinode and a node at the water: three quarter-wavelengths. 3λ/4 = 0.3 m, so λ = 0.4 m and v = fλ = 750 × 0.4 = 300 m s−1.
A 50.0kg block is dropped on a spring from a point 10m as shown in the diagram. If the force constant of the spring is 4.0 × 104 Nm−1, find the maximum compression of the spring. [g = 10ms−2]
Answer: B (0.50m)
Ignoring the small extra drop during compression, mgh = ½ke2: 50 × 10 × 10 = ½ × 4.0 × 104 × e2, so e2 = 0.25 and e = 0.50 m.
In the above diagram, a voltage V is applied across the terminals P and Q. The voltage across the 1 ohms resistor is
Answer: C (V/3)
The two 4 Ω resistors in parallel give 2 Ω, in series with 1 Ω: total 3 Ω. The 1 Ω resistor takes 1/3 of the voltage: V/3.