PHYSICS REVISION WORK

Transcription

1 PHYSICS REVISION WORK 1. When a voltage V of 12.2 V is applied to a DC motor, the current I in the motor is 0.20 A. Which one of the following is the output power VI of the motor given to the correct appropriate number of significant digits? A. 2 W B. 2.4 W C W D W 2. The diagram below shows a boat that is about to cross a river in a direction perpendicular to the bank at a speed of 0.8 m s 1. The current flows at 0.6 m s 1 in the direction shown. The magnitude of the displacement of the boat 5 seconds after leaving the bank is A. 3 m. B. 4 m. C. 5 m. D. 7 m. 1

2 3. The graph shows the variation with time t of the velocity v of an object. Which one of the following graphs best represents the variation with time t of the acceleration a of the object? 4. A ball, initially at rest, takes time t to fall through a vertical distance h. If air resistance is ignored, the time taken for the ball to fall from rest through a vertical distance 9h is A. 3t. B. 5t. C. 9t. D. 10t. 5. A raindrop falling through air reaches a terminal velocity before hitting the ground. At terminal velocity, the frictional force on the raindrop is A. zero. B. less than the weight of the raindrop. C. greater than the weight of the raindrop. D. equal to the weight of the raindrop. 2

3 6. When a body is accelerating, the resultant force acting on it is equal to its A. change of momentum. B. rate of change of momentum. C. acceleration per unit of mass. D. rate of change of kinetic energy. 7. An object of mass m 1 has a kinetic energy K 1. Another object of mass m 2 has a kinetic energy K 2. If the momentum of both objects is the same, the ratio is equal to A.. B.. C.. D.. 8. Which one of the following units is a unit of energy? A. W s B. W s 1 C. W m 1 D. N m s 1 9. A rocket is fired vertically. At its highest point, it explodes. Which one of the following describes what happens to its total momentum and total kinetic energy as a result of the explosion? Total momentum Total kinetic energy A. unchanged increased B. unchanged unchanged C. increased increased D. increased unchanged 3

4 10. Two satellites of equal mass, S 1 and S 2, orbit the Earth. S 1 is orbiting at a distance r from the Earth s centre at speed v. S 2 orbits at a distance 2r from the Earth s centre at speed. The ratio of the centripetal force on S 1 to the centripetal force on S 2 is A.. B.. C. 4. D The graph below shows the variation with displacement d of the force F applied by a spring on a cart. The work done by the force in moving the cart through a distance of 2 cm is A J. B J. C J. D J. 12. Thermal energy is transferred through the glass windows of a house mainly by A. conduction. B. radiation. C. conduction and convection. D. radiation and convection. 13. The specific latent heat of vaporization of a substance is the quantity of energy required to A. raise the temperature of a unit mass of a substance by one degree Celsius. B. convert a unit mass of liquid to vapour at constant temperature and pressure. C. convert a unit mass of solid to vapour at constant temperature and pressure. D. convert a unit mass of liquid to vapour at a temperature of 100 C and a pressure of one atmosphere. 4

5 14. When a gas in a cylinder is compressed at constant temperature by a piston, the pressure of the gas increases. Consider the following three statements. I. The rate at which the molecules collide with the piston increases. II. III. The average speed of the molecules increases. The molecules collide with each other more often. Which statement(s) correctly explain the increase in pressure? A. I only B. II only C. I and II only D. I and III only 15. Water waves at the surface of a pond pass a floating log of length L. The log is at rest relative to the bank. The diagram shows wave crests at one instant. The number of crests passing the log per unit time is N. The speed of the water waves relative to the log at rest is A. (N 1). B. (N 1). C. (N). D. (N). 5

6 16. Two identical triangular pulses of amplitude X travel toward each other along a string. At the instant shown on the diagram below, point M is midway between the two pulses. The amplitude of the disturbance in the string as the pulses move through M is A. 2X. B. X. C. D A person is walking along one side of a building and a car is driving along another side of the building. The person can hear the car approach but cannot see it. This is explained by the fact that sound waves A. travel more slowly than light waves. B. are diffracted more at the corner of the building than light waves. C. are refracted more at the corner of the building than light waves. D. are longitudinal waves. 6

7 18. A pulse is sent down a string fixed at one end. Which one of the following diagrams best represents the reflected pulse? 7

8 19. This question is about an experiment designed to investigate Newton s second law. In order to investigate Newton s second law, David arranged for a heavy trolley to be accelerated by small weights, as shown below. The acceleration of the trolley was recorded electronically. David recorded the acceleration for different weights up to a maximum of 3.0 N. He plotted a graph of his results. (a) Describe the graph that would be expected if two quantities are proportional to one another (b) David s data are shown below, with uncertainty limits included for the value of the weights. Draw the best-fit line for these data. 8

9 (c) Use the graph to (i) explain what is meant by a systematic error. (ii) estimate the value of the frictional force that is acting on the trolley. (iii) estimate the mass of the trolley. (Total 9 marks) 9

10 20. This question is about throwing a stone from a cliff. Antonia stands at the edge of a vertical cliff and throws a stone vertically upwards. The stone leaves Antonia s hand with a speed v = 8.0ms 1. The acceleration of free fall g is 10 m s 2 and all distance measurements are taken from the point where the stone leaves Antonia s hand. (a) Ignoring air resistance calculate (i) the maximum height reached by the stone. (ii) the time taken by the stone to reach its maximum height. The time between the stone leaving Antonia s hand and hitting the sea is 3.0 s. (b) Determine the height of the cliff (3) ` 10

11 21. This question is about the kinematics and dynamics of circular motion. (a) A car goes round a curve in a road at constant speed. Explain why, although its speed is constant, it is accelerating In the diagram below, a marble (small glass sphere) rolls down a track, the bottom part of which has been bent into a loop. The end A of the track, from which the marble is released, is at a height of 0.80 m above the ground. Point B is the lowest point and point C the highest point of the loop. The diameter of the loop is 0.35 m. The mass of the marble is kg. Friction forces and any gain in kinetic energy due to the rotating of the marble can be ignored. The acceleration due to gravity, g = 10 ms 2. Consider the marble when it is at point C. (b) (i) On the diagram opposite, draw an arrow to show the direction of the resultant force acting on the marble. (ii) State the names of the two forces acting on the marble. 11

12 (iii) Deduce that the speed of the marble is 3.0 ms 1. (3) (iv) Determine the resultant force acting on the marble and hence determine the reaction force of the track on the marble. (4) (Total 12 marks) 12

13 22. This question is about equilibrium. Explain whether each of the following is in equilibrium. (a) A satellite in orbit at constant speed round the Earth (b) A small weight suspended on a string and blown to one side by a wind so that the string makes a constant angle with the vertical, as shown below (Total 4 marks) 13

14 23. This question is about waves and wave properties. (a) By making reference to waves, distinguish between a ray and a wavefront (3) The diagram below shows three wavefronts incident on a boundary between medium I and medium R. Wavefront CD is shown crossing the boundary. Wavefront EF is incomplete. (b) (i) On the diagram above, draw a line to complete the wavefront EF. (ii) Explain in which medium, I or R, the wave has the higher speed. (3) (iii) By taking appropriate measurements from the diagram, determine the ratio of the speeds of the wave travelling from medium I to medium R. 14

15 The graph below shows the variation with time t of the velocity v of one particle of the medium through which the wave is travelling. (c) (i) Explain how it can be deduced from the graph that the particle is oscillating. (ii) Determine the frequency of oscillation of the particle. (iii) Mark on the graph with the letter M one time at which the particle is at maximum displacement. (iv) Estimate the area between the curve and the x-axis from the time t = 0 to the time t = 1.5 ms. (v) Suggest what the area in c (iv) represents. (Total 17 marks) 15

16 SOLUTIONS 1. B 2. C 3. A 4. A 5. D 6. B 7. A 8. A 9. A 10. C 11. C 12. A+B 13. B 14. A 15. B 16. D 17. B 18. C 16

17 19. (a) a straight line; through the origin; 2 max (b) any straight line; that fits within ALL the error bars; 2 max (c) (i) a systematic error is when every data point deviates from the correct value; by the same fixed amount as seen by intercept on graph / OWTTE; Accept answers that explain by giving an example of a possible systematic error eg friction. 2 max (ii) 0.3 N; 1 Accept 0.25 N 0.35 N. NB Watch for use of wrong axis (iii) realization that mass = (gradient) 1 ; Award this mark for full Newton II equation (with friction) to give mass = 1.4 kg (Accept 1.2 kg 1.6 kg.); Use of F = ma for 1 data point receives [0] (unless candidate s line is through origin). Watch for ecf from candidate s own line. 2 max [9] 17

18 20. (a) (i) h = ; to give h = 3.2 m; 2 (ii) 0.80 s; 1 (b) time to go from top of cliff to the sea = = 1.4 s; recognize to use s = ut + at 2 with correct substitution, s = (1.4) 2 ; to give s = 21 m; 3 Answers might find the speed with which the stone hits the sea from v = u + at, (42 m s 1 ) and then use v 2 = u 2 + 2as. 21. (a) Look for an answer on the following lines. the direction of the car is changing; hence the velocity of the car is changing; or since the direction of the car is changing; a force must be acting on it, hence it is accelerating; 2 max [6] (b) (i) arrow pointing vertically downwards; 1 (ii) weight; Do not penalize the candidate if they state gravity. normal reaction; 2 Do not penalize the candidate if they state push of the track on the marble. (iii) loss in PE = ( ); = gain in KE = mv 2 ; to give v = 3.0 m s 1 ; or use of v = to give v = 4.0 m s 1 at point B; and then use of v 2 u 2 = 2gh with v = 4.0 m s 1 and h = 0.35 m; to get u = 3.0 m s 1 ; 3 max Do not penalize the candidate if g = 9.8 m s 2 is used. (iv) recognize that resultant force = ; = = 2.6 N; 18

19 N = mg; = = 2.1 N; 4 [12] 22. (a) satellite is accelerating / resultant force towards (centre of) Earth; hence not in equilibrium; 2 (b) sum of forces (in any direction) is zero / OWTTE; hence in equilibrium; 2 [4] 23. (a) ray: direction in which wave (energy) is travelling; wavefront: line joining (neighbouring) points that have the same phase / displacement / Or suitable reference to Huygen s principle; ray is normal to a wavefront; 3 (b) (i) wavefront parallel to D; 1 (ii) frequency is constant; since v = f λ, v λ; wavelength larger in medium I, hence higher speed in medium I; 3 Allow solution based on angles marked on diagram or speed of wavefronts. (iii) ratio = (or based on Snell s law); = = 2.0 allow ± 0.5; 2 (c) (i) velocity / displacement / direction in (+) and ( ) directions; idea of periodicity; 2 (ii) period = 3.0 ms; frequency = = 330 Hz; 2 (iii) Accept any one of the following. at time t = 0, 1.5 ms, 3.0 ms, 4.5 ms, etc; 1 (iv) area of half-loop = 140 ± 10 squares / mean v = 4.0 m s 1 accept ± 0.2; = / ; = m / m; 2 Award for area of triangle. (v) (twice) the amplitude; 1 Allow distance moved in 1.5 m s. [17] 19