Question 1 (7 marks):
a. What are the energy transfers taking place starting from the sun to reach the solar
water heater? (1 mark)
Nuclear to Thermal + Light
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( award one mark if the student mentioned nuclear to thermal or nuclear to light)
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b. If the heater is put inside a room, explain using ideas about particles and heat
transfer how is the air inside the room heated? (2 marks)
any
2 of the mentioned ides:
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the
sun radiates heat, hot air rises, hot air is less dense, cold air sinks, convection current,
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cold
air is more dense
c.
i)
Calculate the power absorbed by the heater. (2 marks)
energy absorbed = 10 000 - 6 000 = 4 000 Joules (1 mark)
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Power = energy / time = 4000 / 200 = 20 Watts ( 1 mark)
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award full mark is the students doesn't mention the formula but substituted the numbers correctly)
ii)
Knowing that the energy absorbed by the heater is the useful energy, Calculate
the efficiency of the heater. (2 marks)
efficiency = E use / E in x 100 = 4000 / 10 000 x 100 = 40 %
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1 mark for formula or substitution, 1 mark for final answer
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Question 2 (10 marks):
B
A
i)
Calculate the work done by the force. (2 marks)
work = force x displacement = 84 x 0.25 = 21 Joules
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(1 mark for formula or substitution, 1 mark for final answer plus unit)
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ii)
Knowing that the push by the brother lasted 1.5 seconds, Calculate the power.
(2 marks)
Power = work / time = 21 / 1.5 = 14 Watts
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(1 mark for formula or substitution, 1 mark for final answer plus unit)
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iii)
What Energy Transfer is taking place as the swing goes from its vertical position
(A) to the maximum height (B)? (1 mark)
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GPE to KE
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(b) The mass of the child is 27 Kg and the speed at A is 4 m/s.
Calculate the Kinetic energy at A. (2 marks)
KE = 1/2 m (v)2 = 1/2 x 27 x (4)2= 216 Joules
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(1 mark for formula or substitution, 1 mark for final answer plus unit)
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c) The child reaches a maximum height of 0.8 m, Calculate the Gravitational Potential
energy at B. (2 marks)
GPE = mgh = 27 x 10 x 0.8 = 216 Joules
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(1 mark for formula or substitution, 1 mark for final answer plus unit)
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d) Compare the values on parts b and c, what can you deduce? (1 mark)
KE at A = GPE at B, Energy is conserved
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Question 3 (7 marks):
(1 mark)
Pressure = Force / area
(2 mark)
Pressure = 720 / (2 x 0.016) = 22,500 Pa
award only one mark if the student didn't multiply the area by 2
22, 500 Pa
(1 mark)
less surface area, more pressure
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(c) The soldier know dives beneath water at a depth of 5m, Knowing that the density of sea
water is 1050 Kg/m3 and the gravity is 10 N/kg and the atmospheric pressure is 100,000 Pa,
Calculate the total pressure exerted on the soldier. (3 marks)
Pressure = density x gravity x depth = 1050 x 10 x 5 = 52,500 Pa
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(1 mark for formula or substitution, 1 mark for final answer plus unit)
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Total pressure = 100,000 + 52,500 = 152,500 Pa (1 mark)
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Question 4 (6 marks):
The following figure represents a Balanced beam.
a) State the equation (word equation) used to calculate the Moment of a force.
(1 mark)
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Moment = Force x perpendicular distance from the pivot
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b) Calculate the total Clockwise Moments . (3 marks)
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( 1 mark)
10 x 1.5 = 15 Nm
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20 x 0.5 = 10 Nm
( 1 mark)
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(1 mark)
Total moments clockwise = 15 + 10 = 25 Nm
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c) Calculate the missing Force (F) knowing that the beam is balanced. (2 marks)
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Moments clock wise = moments anti-clockwise or 25 = F x 0.5 (1 mark)
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F = 25 / 0.5 = 50 N ( 1 mark)
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Good Luck 😊