Questions and Answers
2019 Physics paper 1
Section A: (25 marks)
1. A micrometer screw gauge has a — 0.03 mm error.
State the reading that is observed on the instrument s’hen used to measure the diameter of a wire whose actual diameter is 0.38 mm. (1 mark)
Actual reading = 0.38mm
(error) = 0.03
Meter reading = 0.35mm
2. Figure 1 shows a defective straw used to suck milk from a glass.
It was observed that upon sucking the straw, milk did not rise up the straw. Explain this observation. (2 marks)
- On sucking air rushes into the straw ✔ through the hole making it difficult✔to reduce pressure in the straw by sucking3. State two ways of reducing surface tension of a liquid. (2 marks)
- Using detergents/impurities
- Raising the temperature4. Figure 2 shows a round bottomed flask containing a coloured liquid.
The flask is fitted with a capillary tube.
It is observed that on holding the flask with bare hands, the level of the liquid in the capillary tube initially drops slightly and then rises.
Explain this observation. (3 marks)
The flask absorbs heat from the hands and first expands ✔ hence level of liquid which expands more than the glass causing the rise.
5. figure, 3 shows two metal rods A and B of equal length made of the same material but different diameters.
Wax is attached at one end of each rod .
A source of heat is placed between the two metal rods
- State with a reason, what is observed on the wax. (2 marks)
- Wax on rod B drops off first. The thicker rod conducts heat faster than the thinner one.6.On the axes provided, sketch a displacement — time graph for a trolley moving down a frictionless inclined plane till it reaches the end of the incline.(1 mark)
- 7. A student carrying a heavy box using the right fund is observed to lean towards the left hand side. Explain this observation. (2 marks)
- The box shifts the position of the center of gravity of the system towards the right hand to maintain equilibrium. The student leans in the opposite direction8. Figure 4 shows a one meter long uniform rod of negligible weight supporting two weights.
- Determine the position of the fulcrum from O cm for the rod to remain in equilibrium. (3 marks)Taking moments about the fulcrum Sum of clockwise moments = sum of anticlockwise moments l5x = 10(75 — x (x — 5)10 = (80 — x)15
15x — 750 — l0x 25x = 1250
25x = 750 x = 50cm
x = 30 hence fulcrum at 75 — 30 = 45
45 + 5 = 50
9. State the meaning of the term “radian” as a unit of measurement. ( 1 mark)
- Radian is an angle subtended at the center of a circle by an arc of length equal to the radius of the circle.OR
r = 360/2π
1 radian =
10. For a fluid flowing at a velocity V in a tube of cross-sectional area A, VA = assumptions made in deriving this equation. (2 marks)
(i) Flowing steadily
(ii) Incompressible
(iii) Non-viscous
11. A stone of volume 800 cm3 experiences an upthrust of 6.5 N when fully immersed in a certain liquid. Determine the density of the liquid. (2 marks)
ρ = m/v
ρ = 650g/800cm3
12. Figure 5 shows two springs C and D of the same length and equal number of turns made from the same wire.
State with a reason which of the two springs can support a heavier load before attaining the elastic limit. (2 marks)
C
It has a smaller diameter hence a higher spring constant
13. Two boxes E and F of masses 2.0kg and 4.0kg respectively are dragged along a fictionists surface using identical forces.
State with a reason which box moves with a higher velocity. (2 marks)
E (20N)+
F — Ma, the smaller the mass, the higher the acceleration
SECTION B (55 marks)
Answer all the questions in this section
14. (a) A student is provided with five 20g masses, a meter rule, a spring with a pointer,a stand,a boss and a clamp.
(i) In the space provided, sketch a labelled diagram of the setup that may be used in order to verify Hooke’s law using these apparatus. (3 marks)
- (ii) State two measurements that should be recorded in order to plot a suitable graph so as to verify Hooke’s law. (2 marks)
- Force due to total mass hung.
- Extension produced by hanging masses(iii) Describe how the measurements made in (ii) can be used to determine the spring constant. (2 marks)
- Plot a graph of force against extension.
- Determines the slope of the graph.(b) A helical spring stretches by 0.6 cm when Supporting a weight Of 40 g. Determine the extension when the same spring supports a weight of 65 g. (3 marks)
k =f/e
0.40/0.60
=0.667
e=f/k
65/0.667
0.975cm
15.Figure 6 shows a bottle top opener being used to open a bottle.
15.(a) Indicate on the diagram the direction of the load and the effort. (2 marks)
- (b) State two ways in which an inclined plane can be made to reduce the applied effort when pulling a load along the plane. (2 marks)
- Reducing the angle of inclination.
- Reducing the friction — using rollers, lubricants etc.(c) A block and tackle system has three pulleys in the upper fixed block and two pulleys in the lower movable block.
(i) Draw a diagram to show how the system can be set up in order to lift a load and indicate the position of the load and effort. (3 marks)
- (ii) State the velocity ratio of the set up. (1 mark)(iii) In such a block and tackle system an effort of 200N is required to lift a load of 600 N. Determine its efficiency. (3 marks)
16. (a) State the meaning of the term “heat capacity.” (1 mark)
- Heat capacity is the quantity of heat energy required to raise the temperature of a substance by lK.(b) State how pressure affects the melting point of a substance. (3 marks)
- – Increase in pressure lowers the melting point while decrease in pressure raises/increases the melting point.(C) Figure 7 Shows a set up of apparatus that may be used to measure the specific latent heat of vaporization of stem.
- (i) Describe how the mass of condensed steam is determined. (3 marks)
- Measure the mass of the empty beaker M,.
- Measure the mass of the beaker plus the condensed steam M2
- Get the difference between the two masses(ii) Other than mass and time, state two other measurements that should be taken during the experiment. (2 marks)
- Voltage
- Current(iii) Show how the measurements in (c)(ii) can be used to determine the specific latent heat of vaporisation of water. (2 marks)
- Assuming no heat is lost, Heat produced by heater = Heat used to produce steam Vlt = mLv .‘. Lv = VIT /m(iv) State the precautions that should be taken so that the mass of the condensed steamed measured corresponds to the actual mass of steam collected during the time recorded in the experiment (1 mark)
- Start timing when the steam drops start forming out steadily and Stop immediately the beaker is withdrawn(v) State why it is not necessary to measure temperature in this set up. (1 mark)
- Steam is produced at boiling point where temperature is constant17. (a) State what is meant by Brownian Motion(I mark)
- Continuous random motion of particles.(b) Figure 8 shows the graph of velocity against time for a small steel ball falling in a viscous liquid.
- (i) Describe the motion of the steal ball as represented my port OA. (1 mark)
- It accelerates, velocity increases.(ii) Explain why the velocity between A and B is constant. (3 marks)
- As the ball falls through the fluid, the viscous drag increases until the sum of the viscous drag and the upthrust becomes equal the weight of the steel ball, hence the resultant force becomes zero.(ii) velocity with which the ball hits the ground. 18. (a) Figure 9 shows a graph of pressure against temperature for a fixed mass of gas at constant volume
- From the graph, determine the values of n and c given that P = nT + c where n and c are constants. (4 marks)From y —— mz + c , ( P = nT + C)
– m is the slope of the graph hence n is the slope,
(b) Explain why it is not possible to obtain zero pressure of a gas in real life situation. (2 marks)
- It is not possible to reduce the pressure of a gas to zero since by then most of the temperatures are very low hence the gas liquefies.(c) A fixed mass of a gas occupies 1.5 x 10-3m3 at a pressure of 760 mmHg and a temperature of 273 K.
Determine the volume the gas will occupy at a temperature of 290 K and a pressure of 720 mmHg. (3 marks)
P1V1/T1 = P2V2/T2 ✔
760 x1.5 x 10-3/273 = 760 x V2/290
V2 =760 X 290X1.5 X 10-3/273 X 720
=1.682 X 10-3m
(d) State any three assumptions made in kinetic theory of gases. (3 marks)
- Attraction of between the molecules is negligible.
- Volume of the molecule is negligible compared to the volume of the container occupied by the gas.
- The molecules undergo elastic collisions.
- The length of time of a collision is negligible compared to the time between collisions.
