NSAA 2021 Physics S1

• A.0.750 W
• B.6.75 W
• C.12.0 W
• D.81.0 W
• E.108 W
• F.405 W
• G.1620 W
• H.6480 W

Answer: B

Air is trapped in a cylinder by a piston. The density of the air in the cylinder is $\rho$.

The piston is moved so that the pressure of the trapped air increases by 20%. The temperature of the trapped air does not change.
What is the new density of the trapped air?
(Assume that air is an ideal gas.)

• A.$0.69\rho$
• B.$0.80\rho$
• C.$0.83\rho$
• D.$1.00\rho$
• E.$1.20\rho$
• F.$1.44\rho$

Answer: E

• A.20%
• B.25%
• C.31%
• D.69%
• E.75%
• F.80%
• G.91%
• H.100%

Answer: F

• A.$1.00 \text{ms}^{-2}$
• B.$1.25 \text{ms}^{-2}$
• C.$1.50 \text{ms}^{-2}$
• D.$2.00 \text{ms}^{-2}$
• E.$2.60 \text{ms}^{-2}$

Answer: A

A star is moving away from a space telescope positioned above the Earth. The star emits light of frequency $f$ and wavelength $\lambda$ at the speed of light $c$.
This light travels towards the space telescope through the vacuum of space until it is detected on the space telescope.
The frequency, the wavelength and the speed of the light measured at the telescope are $f_T$, $\lambda_T$ and $c_T$ respectively.
How do $f_T$, $\lambda_T$ and $c_T$ compare with $f$, $\lambda$ and $c$?

• A.$f_T$ equal to $f$, $\lambda_T$ equal to $\lambda$, $c_T$ equal to $c$
• B.$f_T$ equal to $f$, $\lambda_T$ equal to $\lambda$, $c_T$ less than $c$
• C.$f_T$ equal to $f$, $\lambda_T$ greater than $\lambda$, $c_T$ equal to $c$
• D.$f_T$ equal to $f$, $\lambda_T$ greater than $\lambda$, $c_T$ less than $c$
• E.$f_T$ less than $f$, $\lambda_T$ equal to $\lambda$, $c_T$ equal to $c$
• F.$f_T$ less than $f$, $\lambda_T$ equal to $\lambda$, $c_T$ less than $c$
• G.$f_T$ less than $f$, $\lambda_T$ greater than $\lambda$, $c_T$ equal to $c$
• H.$f_T$ less than $f$, $\lambda_T$ greater than $\lambda$, $c_T$ less than $c$

Answer: G

• A.9
• B.16
• C.19
• D.21
• E.25
• F.33
• G.49

Answer: F

A light spring has an uncompressed length of 0.10 m. When an object of mass 0.5 kg rests in equilibrium on top of the spring, the length of the spring reduces to 0.08 m as shown.

What is the energy stored in the spring due to the compression?
(gravitational field strength = $10 \text{Nkg}^{-1}$; the spring obeys Hooke's law)

• A.0.005 J
• B.0.02 J
• C.0.05 J
• D.0.1 J
• E.0.2 J
• F.0.4 J

Answer: C

• A.$\left(\frac{19}{20}\right)^2 P$
• B.$\frac{19}{20} P$
• C.$P$
• D.$\frac{20}{19} P$
• E.$\left(\frac{20}{19}\right)^2 P$

Answer: D

A train accelerates from rest along a straight, horizontal section of track.
The force exerted on the train due to its motors is constant and there is a constant friction force of $1.8 \times 10^7$ N.
The graph shows how the momentum of the train changes with time.

What is the force exerted on the train due to its motors?

• A.$3.0 \times 10^6$ N
• B.$6.0 \times 10^6$ N
• C.$1.2 \times 10^7$ N
• D.$1.5 \times 10^7$ N
• E.$2.1 \times 10^7$ N
• F.$2.4 \times 10^7$ N
• G.$3.0 \times 10^7$ N
• H.$4.2 \times 10^7$ N

Answer: E

• A.$\frac{3}{8}$ m
• B.$\frac{5}{8}$ m
• C.1.0 m
• D.$\frac{11}{8}$ m
• E.24 m
• F.40 m
• G.64 m
• H.88 m

Answer: H

A 6.0 V battery is connected to an 8.0 $\Omega$ resistor and a filament lamp as shown in the circuit diagram.

The reading on the ammeter is 0.25 A.
Which graph is a possible V-I graph for the filament lamp?

• A.Graph A
• B.Graph B
• C.Graph C
• D.Graph D
• E.Graph E
• F.Graph F

Answer: B

A uniform, horizontal magnetic field has magnetic field strength 0.60 T and a direction from west to east.
A horizontal wire is placed in a north-south direction, so that it is at $90^\circ$ to the magnetic field.
The wire carries a constant current.
The wire has length 0.40 m and mass 0.018 kg.
The resultant force acting vertically on the wire is zero.
What are the magnitude and direction of the current in the wire?
(gravitational field strength = $10 \text{Nkg}^{-1}$)

• A.magnitude of current / A: 0.012, direction of current: from north to south
• B.magnitude of current / A: 0.012, direction of current: from south to north
• C.magnitude of current / A: 0.075, direction of current: from north to south
• D.magnitude of current / A: 0.075, direction of current: from south to north
• E.magnitude of current / A: 0.12, direction of current: from north to south
• F.magnitude of current / A: 0.12, direction of current: from south to north
• G.magnitude of current / A: 0.75, direction of current: from north to south
• H.magnitude of current / A: 0.75, direction of current: from south to north

Answer: G

• 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: C

• A.140 s
• B.355 s
• C.430 s
• D.500 s
• E.570 s
• F.860 s
• G.1000 s

Answer: E

A metal block has mass $M$.
Heat is transferred to the block at a constant rate $P$.
The graph shows how the change in temperature $\Delta T$ of the block from its initial temperature varies with time $t$.

The gradient of the line is $k$.
Which expression gives the specific heat capacity of the metal from which the block is made?
(Assume that no heat is transferred out of the block during the time interval shown by the graph.)

• A.$\frac{1}{MPk}$
• B.$\frac{M}{Pk}$
• C.$\frac{Mk}{P}$
• D.$\frac{P}{Mk}$
• E.$\frac{PM}{k}$
• F.$\frac{Pk}{M}$
• G.$\frac{k}{MP}$
• H.$MPk$

Answer: D

• A.600 N
• B.650 N
• C.750 N
• D.790 N
• E.950 N

Answer: B

• A.$\frac{1}{4}$
• B.$\frac{17}{20}$
• C.$\frac{31}{28}$
• D.$\frac{6}{5}$
• E.$\frac{5}{4}$
• F.2

Answer: C

• A.$2.5^\circ$C
• B.$8.3^\circ$C
• C.$10.0^\circ$C
• D.$15.0^\circ$C
• E.$16.7^\circ$C
• F.$22.5^\circ$C

Answer: D

• A.10 Pa
• B.40 Pa
• C.42 Pa
• D.50 Pa
• E.100 Pa
• F.400 Pa
• G.420 Pa
• H.500 Pa

Answer: G

• A.$\frac{t_1}{t_2} L$
• B.$\frac{t_2}{t_1} L$
• C.$\frac{t_1}{2t_2} L$
• D.$\frac{t_2}{2t_1} L$
• E.$\frac{(t_2 - t_1)}{t_2} L$
• F.$\frac{(t_2 - t_1)L}{2t_2}$

Answer: E