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from 0s to 10s, there is a constant acceleration.👌 From 10s to 20s, there is a decreasing acceleration. 👌

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the acceleration is zero constant (cannot be zero acceleration since there is a NET FORCE = 580N )❓ from 0 to 10s and it starts to decrease at a constant rate from 10 to 20s.👌

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1(a) from t=0s to t=10s, acceleration is constant.👌 from t=10s to t=20s, acceleration is decreasing uniformly. 👌

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the acceleration of the bicycle is constant from 0s to 10s but starts to decrease constantly from 10s to 20s  👌

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bi) 3.87m/s^2 square  👌
bii) 40.7m/s  👌

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(b)(i) F=ma
600-20=150a
a=3.87m/s^2 👌

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bi) 3.87 m/s^2  👌
bii) 40.7 m/s  👌

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(b)(ii) a=(v-u)/t
3.87=(v-2.0)/10
38.7=v-2.0
v=40.7m/s  👌

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bi. 3.87m/s^2  👌
bii. 40.7m/s  👌

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(b)F=ma
600N=150a
a=4  ❌ Pls note that the net force = 580 N

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b(ii)600-20=150a
a=v-u/t
v=40.7 ms^-1

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when the height is reduced, the block can tilt more towards the right without toppling over  as the centre of gravity is lowered making the block more stable   👌

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The block can be tilted more before it topples as the centre of gravity will be lower when the height of the block is lowered.  👌

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when the height of the block is reduced, the block can be tilted more to the right without toppling over because its centre of gravity is lower   👌

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(c) Reduced height of the block enables the block to be tilted more before it topples as centre of gravity of the block is lowered.  👌

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P=hpg
=(0.3)(13600)(10)
= 40800 Pa
Pressure of air = 40800 + (1.0)(10^5)
= 140800 Pa ❌

correction : 121760 Pa  👌

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P = hpg
h = 380-220
= 160mm
= 0.16m
P = (0.16)(13600)(10)
= 21760 Pa
Pressure of the air in the flask
= 21760+ (1.0 x 10^5)
= 121760 Pa  👌

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3(a) P(air)= P(atm) + P(mercury)
= 1.0*10^5 + hpg
= 1.0*10^5 + (0.38-0.22)(13600)(10)
=121760Pa  👌

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121760 Pa  👌

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Work is the product of the force and distance moved by the object towards the direction of the force

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work is the product of the force and the distance moved by the object in the direction of the force

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3b) when the air in the flask starts to cool, it’s temperature decreases and hence the molecules move slower (have less KE) and hit the walls of the flask less frequently and with lesser force . this causes the air pressure to decrease and therefore, the mercury level decreases.  👌

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24 degree celsius  👌👌

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3(b) lower temperature of air in the flask decreases the kinetic energy of gas molecules. frequency of collisions between the molecules and the walls of the container decreases and with less force, pressure of gas molecules decreases, resulting in a decrease in mercury levels  👌

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Q3Work done is energy taken for a specific force  to move an object over a distance.

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4(a) work done is the product of the force and distance moved by the object in the direction of the force.

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4a) Work is the force multiplied by the distance travelled in the direction of the force.

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4(b)
GPE at B = KE at C
mgh = 1/2 mv^2
10(12) =1/2 v^2
v^2 = 240
v = 15.5 m/s (3d.p.)

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15.5m/s (3sf)

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100 J

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the cold junction is placed in an unknown liquid with unknown temperature, thus, the temperature of the surrounding air cannot be determined as the temperature of one junction have to be known to determine the temperature of the other junction. 👍👍

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24 deg C ✔

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5i) the cold junction is placed in a liquid of unknown temperature and hence, knowing the potential difference will not help in identifying the temperature of the surrounding air because it can only be determined when the temperature of the liquid is known. 👍👍

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5(a)(i)
The final temperature of the liquid is not known hence the decrease in thermocouple reading cannot be used to identify the temperature of the surrounding air, 👍👍

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5ii) 24 deg c ✔

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5(ii)
24 degrees celsius ✔

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5b) when the walls of the capillary are not uniform, this causes the area of the capillary to be bigger and hence, when the liquid in the thermometer rises up, the reading on the thermometer will be lower than it is supposed to be, giving an inaccurate temperature reading. 👍👍👍

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5(b)
There is a difference in diameter of the capillary hence, there is greater pressure ❓❓ on the lower part of the thermometer, hence increasing ❌ (decreasing) the height of volume of liquid in the thermometer, giving an inaccurate reading. 👌👌

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6a) frequency = 4.17 x 10^14 Hz ✔✔
(Note: Don't forget the unit)

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6bi) infra-red rays ✔

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6bii) remote control of electrical appliances  ✔

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7ai) angle of incidence = 41.7 deg (1dp) ❌ 22.1 degrees

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7aii) R2 does not exit the bottle after the first refraction because it undergoes total internal reflection where its angle of incidence is greater than the critical angle. 👍👍 (also mention that light is travelling from denser medium into less dense medium)

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7b) Total internal reflection will occur in the bottle. Hence, the light rays entering the bottle will be able to exit through the base of the base of the bottle and light up large parts of the house interior. Without the bottle, sunlight can only reach parts of the house.

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7c) radiation. the sun's energy travels to earth as electromagnetic waves which is known as infra-red radiation. when absorbed, the energy of the infra-red radiation transforms into thermal energy of the receiving body. (can pass through vacuum)

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8bi) steel ❌ Soft iron (speakers need to constantly magnetise and demagnetise to vibrate the cone of the speakers to produce sound)

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8bii) steel is a hard magnetic material and hence it is difficult to lose its magnetism once magnetised, making it a permanent magnet. thus, it is suitable.

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9a)
Minimum distance = 500 x 10^-6 x 330
= 0.165m ❌ Distance = 1/2 x 0.165m = 0.0825 m (since 0.165m is the distance travelled by sound and its echo)

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9b)
Minimum distance = 3 x 10^8 (This is speed of light not sound) x 500 x 10^-6 = 150000m  ❌ 75000 m

The equipment which transmits and receives radio waves would be more useful because it can detect the time delay from a greater distance. huh? The radio wave version detects shorter distance but more appropriate compared to detecting wall from 75 km away?!

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10a) V=IR
Current through Lamp 3 = 7.60 - 1.90 = 5.70A
Resistance of Lamp 3 = 200/ 5.70 = 35.1 ohms (3sf) 👌👌

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10b)
R1 = 200/0.4 = 500 ohms
R2 = 200/1.5 = 133 ohms
R3 = 35.1 ohms
effective resistance = 26.3 ohms
power = (7.60^2) (26.3) = 1519.088W
energy used = 1519.088 x 110/60 x 7 = 19494.96267 Wh
= 195 kWh
cost = 19.5 x 0.22 = $4.29 (nearest cent) 👍👍

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11ai)
200MJ = m x 4.2 x 10^3 x (25-14) --> change in temp is (45-25)
200 x 10^6 = m x 4.2 x 10^3 x 11
m = (200 x 10^6) / (4.2 x 10^3 x 11)
m = 4329.004
m = 4330 kg (3sf)  ❌ 2380 kg

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total solar energy = 110x10^6 J (3sf)❌ 310 MJ

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11b) the average daily sunshine duration for Fiji is only 4 hours a day. solar energy is used for heating up the interior of the house. with only 4 hours of sunshine a day, the solar energy absorbed is insufficient for maintaining the indoor temperature at 25 deg c for Fiji 👍👍 Fiji will need (7.17 x 0.84) = 6 hrs of sunshine

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11c) steel. steel is dark-coloured (what?! Steel is silver in colour, you can use black paint to get it dark) and hence, it is a good absorber of infra-red radiation. this will allow a lot of sunlight to be absorbed to maintain the indoor temperature of the house. Just state that it is a good conductor of heat.

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12a) ohm's law states that the current through a metallic conductor is directly proportional to the potential difference across the ends of the conductor, provided the temperature and other physical conditions remain constant.

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12b) the filament lamp does not obey ohm's law because its resistance increases as the current increases

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12c) the resistance of the lamp increases when the potential difference is increased. V=IR when V and I are both increasing, R will also increase.

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12di) variable resistor

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12dii) a variable resistor has a fixed resistance and hence, current has to pass through it first before passing through the lamp. this will decrease the current through the lamp.

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12ei) electrical current = 0.05A (from the graph)

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12eii)
V = IR
2.5V = I x 200 ohms
I = 2.5/200
I = 0.0125A

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13 (either)
a) current is flowing from A to D. using Fleming's left-hand rule, the magnetic field represented by the index finger is pointing to the left. the middle finger which represents the current is pointing into the paper and hence current flows from A to D.

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13c) commutator. the commutator rotates together with the coil. it allows the coil to rotate by reversing the current in the coil in every half-turn

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13d) using stronger magnets, increasing the number of turns of the coil, increasing the current flow and winding the coil around a soft-iron cylinder

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13 (or)
ai) positive

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13aiii) the tension in the string

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13bi) the negative charges of the sphere will flow to the ground, leaving the positive charges

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13bii) the sphere will move further away from the plate because they are both positively charged and hence, they repel

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6(a) frequency = 4.17 x 10^14 Hz ✔
6(b)(i) Infra-red rays ✔
6(b)(ii) Used in lasers ❓❓ (laser is a different technology)
Infra-red is used in remote control, heating elements, intruder alarms)

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Infrared ray ✔

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a) 4.17 x 10^14 Hz ✔
bi) infrared ✔
bii) infrared cooker ✔

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treating skin injuries 👌 (Note: This application is quite rare e.g. applicable to burn victims so better to name more common applications like remote control, burglar alarm or heating element)

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22.1 deg ✔

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Total internal reflection occurs, as the ray is travelling from a denser medium to a less dense medium, and the angle of incident is larger than the critical angle. ✔ (excellent answer)

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ai) 22.1 degree celsius 👍👍
aiii) The angle experiences total internal reflection as the angle of incidence is greater than the critical angle   👍👍   (also mention that light is travelling from denser medium into less dense medium)

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As total internal reflection will occur in the bottle, the bottle can trap light, thus, lighting up the room better than just the plastic sheet. (Not really "trap" light but allows more light to exit via the bottom half of the bottle)

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Radiation. Heat is transferred as a form of infrared radiation from the sun to the boy. (can pass through vacuum)

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Steel ❌ Soft iron (speakers need to constantly magnetise and demagnetise to vibrate the cone of the speakers to produce sound)

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Steel is a hard magnetic material, which is suitable for making permanent magnet as it is hard for steel to lose its magnetism.❌

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8(a)(i) magnetic field lines on the left and right and drawn curving into the opposite end of the north pole of the magnet 👍👍
8(a)(ii) X is located in between the two magnets. 👍👍

8(b)(i) Steel ❌ Soft iron (speakers need to constantly magnetise and demagnetise to vibrate the cone of the speakers to produce sound)

8(b)(ii) Steel has ferromagnetic properties, hence it is difficult to lose its magnetism after being magnetized, making it a permanent magnet,

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0.165 m ❌ Distance = 1/2 x 0.165m = 0.0825 m (since 0.165m is the distance travelled by sound and its echo)

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7(a)(i) Incidence angle = 22.1 degree celcius ✔
7(a)(ii) Angle of incidence greater than critical angle, hence total internal reflection occurs and R2 does not exit the bottle (also mention that light is travelling from denser medium into less dense medium) 👍👍
7(b) not sure
7(c) Radiation. Thermal energy is transferred in the form of electromagnetic waves and the infra-red radiation produces a warm feeling on the boy since only radiation can pass through vacuum to reach Earth from the sun.

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bi) steel  ❌ Soft iron (speakers need to constantly magnetise and demagnetise to vibrate the cone of the speakers to produce sound)

bii) Steel is a hard magnetic material which is suitable for making a permanent magnet as steel does not lose its magnetism easily

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The new equipment is more useful as it can detect the time delay at a further diatance compared to the other equipment.
minimum dist. of new equipment ❌ The minimum distance of 75000m is too far and impractical for carpark lot distances.

= (3.0)(10^8) (500)(10^-6) / 2
=75000m 👍👍

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35.1 ohms (3sf) 👌👌

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9(a) Minimum distance = 330 x 500 x 10^-6
= 0.165m ❌ Distance = 1/2 x 0.165m = 0.0825 m (since 0.165m is the distance travelled by sound and its echo)

9(b) Minimum distance
= 3 x 10^8 x 500 x 10^-6
= 150000m ❌ 75 000m

The equipment transmitting radio waves is more useful as there is a greater minimum distance to detect the time delay. huh? The radio wave version detects shorter distance but more appropriate compared to detecting wall from 75 km away?!

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a) 0.165m ❌ Distance = 1/2 x 0.165m = 0.0825 m (since 0.165m is the distance travelled by sound and its echo)

Reason: ??

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a)35.1 ohms  👌👌
b) $4.29  ✔

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10(a) Resistance of lamp 3 = 35.1 ohms (3s.f.) 👌👌

10(b) Cost = $4.29 (2.d.p.) ✔

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$4.29 (nearest cent) 👍👍