**2018 Physics paper 1**

**Section A: (25 marks)**

**1. State the reason why an **object** on earth has a higher weight than on the moon. (1 mark)**

Earth’s gravity is higher than the moon’s gravity

**2. Figure 1 shows the position of a students cye while illustrate the length of a wooden block using a theme rule.**

**Determine the 1cngth of’the block as viewcd by the student. (1 mark)**

7.3 —6.0 = 1.3cm

**3. Describe how the knowledge of the oil drop experiment may be used to estimate the area of oil spillage from a ship in the sea assuming the sum face water is not distort bed. (3 marks)**

- Using the same oil spilled, to measure a known volume.
- Determine the area of spread of the measured volume (on the same water (sample).
- Estimate the area of spread on the sea.
**4. Figure 2 shows an instrument used to measure atmospheric pressure.**

**(a) State with a reason the modification that would be required in a similar set up if mercury were to be replaced with water. (2 marks)**

The tube will be very long since water has much lower density than mercury

**5. It is observed that a drop of milk carefully put into a cup of water tums the water white after some time. State the reason for this observation. (1 mark)**

Milk particles move to occupy the spaces between the water particles through diffusion.

**6. Figure 3 shows the shape of a bimetallic strip after it was cooled below room temperature.**

**Explain why the strip curved is as shown. (2 marks**

**)**

Brass contracts more than invar hence contracts leaving the side with invar longer hence the curve.

**7. A wooden cube of side 0.5m floats in water frilly submerged. Determine the weight of’the cube.density of the water = 1gm ^{-3}).(2 marks)**

Volume of water displaced = 0.5 x 0.5 x 0.5

= 0. l25m^{3}

W of cube. — weight of water displaced (a floating body)

= lx 125000g

= l25kg

= 1.25 x 10^{3}N

**8. Figure 4 shows a stonc whirled in a veitical circle.**

**On the axes provided, sketch a graph of tension against time as the stone moves through point A, B, C and D. (3 marks)**

**(a) On the diagram, sketch the path followed by the ball as it moves.(1 mark)**

**(b) Explain why the ball takes that path.(3 mark)**

Because of Bemoullis effect caused by diference in air pressure due to the streamlines. As the ball moves to the right airstreams move to the left . Spin is anti-clockwise, a region of low pressure forms above lifting the ball.

**10. Figure 6 shows the relationship between volume and pressure for a certain gas.**

**Name the law that the gas obeys (1 mark)**

Boyles law

**11. Figure 7 shows an L-shaped wooden structure.**

**On the diagram construct appropriate lines to show the position of’ the centre of gravity for the structrne. (2 marks)**

**12. Figure 8 shows the graph of extension against force for a certain helical spring.**

**On the same diagram sketch the graph of extension against force for a spring with a lower value of spring constant. (1 mark)**

**13. State two ways in which a mercury based thermometer can be modified to read very small temperature changes. (2 marks)**

- Making the bulb thinner.
- Making the bore narrower.
**SECTION B (55 marks)****14. (a) State two differences between boiling and evaporation.(2 marks)** - Boiling takes place at fixed temperature while evaporation takes at all temperatures.
- Boiling takes place in the entire liquid while evaporation takes place at the surface.
**(b) State three ways in which loss of heat by conduction is minimised in a vacuum flask. (3 marks)** - Presence of a vacuum.
- Poor conductor material used to make stopper.
- Use of glass (poor conductor).
**(c) In a certain experiment, 50 g of dry steam at 100°C was directed into some crushed ice at 0 °C. (Latent heat ofvoporisation of water is 2.26 X 10**^{6}Jkg-I. latent heat of;fusion fi)r ice is 3.34 X 105 Jkg-/ and specific heat capacity of water is 4.2 X 10^{3}Jkg-‘) Determine the:**(i) quantity of heat lost by steam to change to water at 100 °C.(2 marks)**Heat lost by steam at 100°C.

ML

_{v}=5.0 x 10^{-2}x2.26×10^{6}= 11.3 x 10

^{4}1.13 x 10

^{5}J**(ii) quantity of heat lost by water to cool to 0°C.(2 marks)**Heat lost by hot water to cool to 0°C.

MCAθ = 5.0 x 10

^{-2}x 4.2 x 10^{3}x 10^{2}= 2.1x 10

^{4}J**(iii) mass of ice melted at 0 °C.(2 marks)**Amount of ice melted at 0°C.

M

_{iceLf = Mlv+MCA8}M= 2.1x 10

^{4}+1.13 x10^{5}/ 3.34 x 10^{5 = 0.401kg.}— 401g

**15. (a) State Newton’s fiist law’ of motion. (1 mark)** - A body remains in its state of rest or uniform motion in a straight Line unless acted upon by an external force.
**(b) A wooden block resting on a horizontal bench is given an initial velocity u so that it slides on the bench for a distance x before it stops.****Various values of x are measured for different alnes of’tlie initial velocity. Figure 9 shows a graph of u<sup2< sup=””> against x.</sup2<>**

**(i) Determine the slope S of the graph. (3 marks)**(i) Slope = ∆U^{2}/∆x= 50 — 0/8-06.25

**(ii) Determine the value of k given that u**^{2}= 20kd where k is a frictional constant for the sui tacc. (2 marks)(ii) U

^{2}/x = 20k butU^{2}/x= slopeK=slope/20

6.25/20

K = 0.3125

**(iii) State with a reason what happens to the value of k when the roughness of the bench surface is reduced. (2 marks)**- K would reduce since friction has reduced(c) An object is thrown vertically upwards with an initial velocity of 30 ms ‘. Determine its maximum height (acceleration due to gravity g is 10 mw’). (3 marks)Hmax =u
^{2}/2g =30 x 30/2 x 10 90/2 = 45m**16. (a) An electie crane uses 8.0 x 10‘ N of energy to lift a load of 2.0 X 104 N in 4 s.****( i) Determine the****power developed by the crane,(3 marks)**power = Work done

time =80000 /4

= 20000W

**(ii) height to which the load is lifted, (2 marks)**d = work/force

80000/20000

= 4 m

**(iii) efficiency of the crane whose motor is rated 2.5 X 10’W. (2 marks)** - Efficienc Workoutput/workinput x 10020000/25000×100=80.00%
**iii) Sure two forms of energy transformation that lead to the crane’s inefficiency. (2 marks)** - Mechanical energy
- heat and sound
**(b) A stone is dropped from the top of a building to the ground. On the axes provided, sketch a graph of potential enemy against time for the stone. (1 mark)**

**17. (a) State Pascal’s principle of transmission of pressure in liquids.**

Pressure applied at one part in a liquid is transmitted equally to all other parts of the enclosed liquid.

**(b) Figure 10 shows heights of two immiscible liquids X and Y in a U-tube (drawn to scale).**

**(i) State with a reason which of the two liquids X and Y has a higher density. (2 marks)**Liquid y is denser since it rises to a smaller height i.e. atmospheric pressure supports a lower height of y than x**(ii) Determine the value of h. (2 marks)**(ii) h = 2.2/3.6 x 20

=12.22cm

**iii) Given that the density of liquid Y is p, write down an expression for the density d of liquid x in terms of p. (2 marks)**d/p = 3.6/2.2 = 1.636

d=1.6p

(c) ( i) With the aid of a diagram, describe how a liquid may be siphoned from one container to another using a flexible tube. (3 marks)

**iii) Sums one application of the siphon. (1 mark)**- The flushing of a toilet
- Drinking using a straw.
**18. (a) State two quantities that must be kept constant in order to verify Boyle’s law. (2 marks)** - Mass
- Temperature
**(b) An air bubble at the bottom of a beaker full of water becomes larger as it rises to the surface. State the reason why;** - The gas is less dense than the water.
- As it rises the pressre around the bubble reduces and since the temperature is the same, the volume increases
**(i) the bubble rises to the surface,(1 marks)** - The gas is less dense than the water.
**(ii) it becomes larger as it rises.(1 marks)** - As it rises the pressre around the bubble reduces and since the temperature is the same, the volume increases
**(c) State two assumptions made in explaining the gas laws using the kinetic theory of gases.(2 marks)** - The size of the molecules is assumed to be neglibible.
- Intermoleeular forces are also assumed to be negligible.
- Real gases can never have zero volume yet the gas laws assume presence of zero volume(d) Figure 11 shows an incomplete experimental set up that was prepared by a student to verily one of the gas laws.Thermometer Pressure gauge

**(i) State with a reason which one of the laws may be verified using the set up. (2 marks)**- The pressure law.
- Has ability to measure the temperature and the pressure while keeping the volume constant
**(ii) State what the student left out in the diagram of the set up. (1 mark)** - Source of heating for the temperature to be changedm
**(e) The volume of a fixed mass of a gas reduced from 500 cm**V^{3}to 300 cm^{3 }at constant pressure. The initial temperature was 90K. Determine the final temperature. (3 marks)_{1}/T_{1}= V_{2}/T_{2}T

_{2}=300 x 90/500= 54k