NSAA 2018 Physics PART B

• A.6
• B.8
• C.10
• D.12
• E.14
• F.16
• G.18
• H.20

Answer: B

The diagram shows three resistors $R_1$, $R_2$ and $R_3$ connected in series with a battery of constant voltage. The resistance of each resistor and the corresponding current are also shown.

[Image of a series circuit with a battery, an ammeter showing 0.20 A, and three resistors: R1 = 12Ω, R2 = 15Ω, R3 = 3.0Ω]

Resistor $R_3$ is now removed and the circuit is reconnected.

What is the new current in the circuit?

• A.0.20 A
• B.0.22 A
• C.0.33 A
• D.0.40 A
• E.0.50 A
• F.2.0 A
• G.6.0 A

Answer: D

• A.It has a maximum frequency of $2.7 \times 10^{14}$ Hz
• B.It has a maximum frequency of $4.3 \times 10^{14}$ Hz
• C.It has a maximum frequency of $7.5 \times 10^{14}$ Hz
• D.It has a maximum frequency of $1.0 \times 10^{15}$ Hz
• E.It has a minimum frequency of $2.7 \times 10^{14}$ Hz
• F.It has a minimum frequency of $4.3 \times 10^{14}$ Hz
• G.It has a minimum frequency of $7.5 \times 10^{14}$ Hz
• H.It has a minimum frequency of $1.0 \times 10^{15}$ Hz

Answer: G

The graph is the speed-time graph for a bus travelling in a straight line between two stops.

[Image of a speed-time graph with speed/ms⁻¹ on the y-axis and time/s on the x-axis. The graph shows acceleration from (0,0) to (20,12), constant speed from (20,12) to (80,12), and deceleration from (80,12) to (120,0).]

What is the average speed of the bus during this time?

• A.$3.0 \text{ms}^{-1}$
• B.$4.5 \text{ms}^{-1}$
• C.$6.0 \text{ms}^{-1}$
• D.$8.0 \text{ms}^{-1}$
• E.$9.0 \text{ms}^{-1}$
• F.$11 \text{ms}^{-1}$
• G.$12 \text{ms}^{-1}$

Answer: E

• A.50 J
• B.950 J
• C.1000 J
• D.3000 J
• E.57 000 J
• F.60 000 J

Answer: E

• A.$P \propto \frac{(T_1 - T_2)}{Al}$
• B.$P \propto \frac{(T_1 + T_2)}{Al}$
• C.$P \propto \frac{A(T_1 - T_2)}{l}$
• D.$P \propto \frac{A(T_1 + T_2)}{l}$
• E.$P \propto \frac{l}{A(T_1 - T_2)}$
• F.$P \propto \frac{l}{A(T_1 + T_2)}$
• G.$P \propto \frac{Al}{(T_1 - T_2)}$
• H.$P \propto \frac{Al}{(T_1 + T_2)}$

Answer: C

• A.225 000 J
• B.500 000 J
• C.900 000 J
• D.1 250 000 J
• E.2 000 000 J

Answer: C

• A.3.0 kg
• B.4.0 kg
• C.6.0 kg
• D.8.0 kg
• E.12 kg

Answer: A

A radioactive isotope decays in a single step to a stable isotope.

A radiation detector is placed very near to a sample of the radioactive isotope in a laboratory. The count rate on the detector changes as time elapses. The graph shows how the measured count rate changes with time.

[Image of a decay graph showing count rate vs. time. The count rate starts at 120 counts per minute at time 0 and exponentially decays, asymptotically approaching 20 counts per minute.]

What is the background count rate and what is the half-life of the isotope?

• A.background count rate / counts per minute: 20, half-life of isotope / minutes: 40
• B.background count rate / counts per minute: 20, half-life of isotope / minutes: 50
• C.background count rate / counts per minute: 20, half-life of isotope / minutes: 60
• D.background count rate / counts per minute: 20, half-life of isotope / minutes: 65
• E.background count rate / counts per minute: 120, half-life of isotope / minutes: 40
• F.background count rate / counts per minute: 120, half-life of isotope / minutes: 50
• G.background count rate / counts per minute: 120, half-life of isotope / minutes: 60
• H.background count rate / counts per minute: 120, half-life of isotope / minutes: 65

Answer: A

• A.1.0 kg
• B.1.2 kg
• C.1.5 kg
• D.6.0 kg
• E.10 kg
• F.12 kg
• G.15 kg
• H.60 kg

Answer: C

• A.2.4 m
• B.4.8 m
• C.8.0 m
• D.16 m
• E.32 m
• F.48 m

Answer: E

• A.18 g
• B.20 g
• C.90 g
• D.180 g
• E.200 g

Answer: C

A skydiver of weight 1000 N falls vertically.

The distance-time graph for the skydiver is shown below.

[Image of a distance-time graph where the slope gradually increases and then becomes constant, indicating terminal velocity.]

The air resistance $F$ (in N) acting on the skydiver travelling at velocity $v$ (in $\text{ms}^{-1}$) is given by the equation

$$F = kv^2$$

where $k$ (in $\text{Nm}^{-2}\text{s}^2$) is a constant.

What is the numerical value of $k$ for the skydiver?

• A.0.050
• B.0.40
• C.0.63
• D.2.5
• E.20

Answer: B

• A.$42 \text{cms}^{-1}$
• B.$50 \text{cms}^{-1}$
• C.$54 \text{cms}^{-1}$
• D.$60 \text{cms}^{-1}$
• E.$72 \text{cms}^{-1}$
• F.$90 \text{cms}^{-1}$

Answer: E

• A.neutrons: 2, protons: 55
• B.neutrons: 2, protons: 56
• C.neutrons: 2, protons: 57
• D.neutrons: 2, protons: 58
• E.neutrons: 3, protons: 55
• F.neutrons: 3, protons: 56
• G.neutrons: 3, protons: 57
• H.neutrons: 3, protons: 58

Answer: H

The diagram shows a circuit containing a battery and three identical resistors X, Y and Z.

[Image of a circuit diagram where resistor Z is in series with a parallel combination of resistors X and Y, all connected to a battery.]

The total power supplied by the battery is 18 W.

What is the power dissipated as heat in resistor X?

• A.1.5 W
• B.2.0 W
• C.3.0 W
• D.4.5 W
• E.6.0 W
• F.8.0 W
• G.12 W

Answer: C

A filament lamp and a 0-10Ω variable resistor are connected in series with a power supply of constant voltage.

The graph shows the voltage-current (V-I) characteristic of the filament lamp.

[Image of a non-linear V-I graph for a filament lamp, with Voltage (V) on the y-axis and Current (A) on the x-axis. The curve starts at the origin and curves upwards.]

When the resistance of the variable resistor is 4.0Ω, the current in the lamp is 2.0 A.

What is the power dissipated in the lamp when the resistance of the variable resistor is zero?

• A.12 W
• B.14 W
• C.16 W
• D.28 W
• E.42 W
• F.96 W

Answer: E

• A.none of them
• B.1 only
• C.2 only
• D.3 only
• E.1 and 2 only
• F.1 and 3 only
• G.2 and 3 only
• H.1, 2 and 3

Answer: A