Physics form six Past paper for NECTA 2016 Academic year
SECTION A (40 Marks)
Answer four (4) questions from this section.
1: (a) (i) Define the term dimension of a physical quantity. (1 mark)
(ii) The number of particles n crossing a unit area perpendicular to x-axis in a unit time is given as n = -D where n1 and n2 are the number of particles per unit volume for (x −x ) 2 1(n −n ) 2 1 the values of x1 and x2 respectively. What are the dimensions of diffusion constant D? (1 mark)
(b) (i) Give two basic rules of dimensional analysis. (1 mark)
(ii) The frequency, f of a vibrating string depends upon the force applied, F the length, l of the string and the mass per unit length, 𝜇. Using dimension show how f is related to F, l and 𝜇. (2.5 marks)
(c) (i) What is meant by least count of a measurement? (1 mark)
(ii) The period of oscillation of a simple pendulum is given by T = 2𝜋 where by 100 √lg vibrations were taken to measure 200 seconds. If the least count for the time and length of a pendulum of 1m are 0.1sec and 1mm respectively, calculate the maximum percentage error in the measurement of g. (2.5 marks)
2: (a) (i) Mention two characteristics of projectile motion. (1 mark)
(ii) If the range of the projectile is 120m and its time of flight is 4sec, determine the angle of projection and its initial velocity of projection assuming that the acceleration due to gravity g = 10ms-2 (3 marks)
(b) (i) State the principles on which the rocket propulsion is based. (1 mark)
(ii) A jet engine on a test bed takes in 40kg of air per second at a velocity of 100ms -1 and burns 0.80kg of fuel per second. After compression and heating the exhaust gases are ejected at 600ms -1 relative to the aircraft. Calculate the thrust of the engine. (2 marks)
(c) An object of mass 2kg is attached to the hook of a spring balance which is suspended vertically to the roof of a lift. What is the reading on the spring balance when the lift is:
(i) going up with the rate of 0.2ms-2 (1 mark)
(ii) going down with an acceleration of 0.1ms-2 (1 mark)
(iii) ascending with uniform velocity of 0.15ms-1 (1 mark)
3: (a) (i) Define the term inertia. (1 mark)
(ii) Why is Newton’s first law of motion called the law of inertia? (1 mark)
(b) A jet of water from a fire hose is capable of reaching a height of 20m. If the cross sectional area of the hose outlet is 4.0×10-4m2 calculate the
(i) Minimum speed of water from the hose. (1 mark)
(ii) Mass of water leaving the hose each second. (2 marks)
(iii) Force on the hose due to the water jet. (2 marks)
(c) A boy ties a string around a stone of mass 0.15kg and then whirls it in a horizontal circle at
constant speed. If the period of rotation of the stone is 0.4sec and the length between the stone
and the boy’s hand is 0.50m;
(i) Calculate the tension in the string. (2.5 marks)
(ii) State one assumption taken to reach the answer in 3 (c) (i) (0.5 mark)
4: (a) What do you understand by the following terms:
(i) Damped oscillations. (1 mark)
(ii) Undamped oscillations. (1 mark)
(b) (i) Sketch the waveform diagrams to represent the terms in 4 (a) (i). (2 marks)
(ii) Show that the total energy of a body executing S.H.M. is independent of time. (2 marks)
(c) A mass of 0.5kg connected to a light spring of force constant 20Nm-1 oscillates on a horizontal frictionless surface. If the amplitude of the motion is 3.0cm, calculate the;
(i) Maximum speed of the mass. (2 marks)
(ii) Kinetic energy of the system when the displacement is 2.0cm. (2 marks)
5: (a) (i) What is meant by moment of inertia of a body? (1 mark)
(ii) List two factors on which the moment of inertia of a body depends. (1 mark)
(b) A thin sheet of aluminium of mass 0.032kg has the length of 0.25m and width of 0.1m. Find its moment of inertia on the plane about an axis parallel to the;
(i) Length and passing through its centre of mass m. (2 marks)
(ii) Width and passing through the centre of mass m in its own plane. (2 marks)
(c) (i) Define the term angular momentum. (1 mark)
(ii) A thin circular ring of mass M and radius r is rotating about its axis with constant angular velocity 𝜔1
. If two objects each of mass m are attached gently at the ring, what will be the angular velocity of the rotating wheel? (3 marks)
6: (a) (i) Mention one application of parking orbit. (1 mark)
(ii) Briefly explain how parking orbit of a satellite is achieved? (1.5 marks)
(b) The earth satellite revolves in a circular orbit at a height of 300km above the earth’s surface. Find the;
(i) Velocity of the satellite. (2 marks)
(ii) Period of the satellite. (1.5 marks)
(c) (i) Why are space rockets usually launched from west to east? (1.5 marks)
(ii) A spaceship is launched into a circular orbit close to the earth’s surface. What additional velocity has to be imparted to the spaceship in order to overcome the gravitational pull? (2.5 marks)
SECTION B (30 Marks)
Answer three (3) questions from this section.
7: (a) Briefly explain why:
(i) A body with large reflectivity is a poor emitter. (1 mark)
(ii) The earth without its atmosphere would be too cold to live. (1 mark)
(b) (i) Identify two factors on which the coefficient of thermal conductivity of a material depends. (1 mark)
(ii) A brass boiler of base area 1.50×10-1m2 and thickness of 1.0cm boils water at the rate of 6.0kg/min when placed on a gas stove. Estimate the temperature of the part of the flame in contact with the boiler. (2.5 marks)
(c) (i) Briefly describe the working principle of a thermocouple. (2 marks)
(ii) In a certain thermocouple thermometer the e.m.f. Is given by E = a𝜃 + ½ b𝜃 2 where 𝜃 is the temperature of hot junction. If a = 10mV°C-2, b = mV°C-1 − and the cold junction is120 at 0°C, calculate the neutral temperature. (2.5 marks)
8: (a) (i) What is meant by thermal radiation? (1 mark)
(ii) Briefly explain why forced convection is necessary for excess temperature less than 20K? (1.5 marks)
(b) (i) Why is the energy of thermal radiation less than that of visible light? (1.5 marks)
(ii) A body with a surface area of 5.0cm 2 and a temperature of 727°C radiates 300 joules of energy in one minute. Calculate its emissivity. (2 marks)
(c) (i) State Newton’s law of cooling. (1 mark)
(ii) A body cools from 70°C to 40°C in 5 minutes. If the temperature of the surroundings is 10°C , Calculate the time it takes to cool from 50°C to 20°C. (3 marks)
9: (a) (i) Define the term junction as applied in electrical networks. (1 mark)
(ii) What is the physical significance of Kirchhoff’s first law? (1 mark)
(b) (i) Why is Kirchhoff’s second law sometimes referred to as the voltage law? (1 mark)
(ii) List down five points to be considered when applying Kirchhoff’s second law in formulating analytical problems or equations. (2.5 marks)
