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S3 Physics -. Forces 1. 1. 2. 3. 4. 5. 6. 7. 10. 11. 12. 13. 14. 8. 9. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. answer. 1. What two measurements are needed to calculate the average speed of an object?. Distance and Time. answer.

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## S3 Physics -

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**S3 Physics -**Forces 1 1 2 3 4 5 6 7 10 11 12 13 14 8 9 15 16 17 18 19 20 21 22 23 24 25 26**answer**1. What two measurements are needed to calculate the average speed of an object? Distance and Time**answer**2. What equation would be used to calculate average speed? Speed = distance / time**answer**3. A trolley takes 1.5 s to travel 60cmCalculate its average speed.. v = d/t = 60 / 1.5 = 40 cm/s**answer**4. Does a car speedometer give average or instantaneous speed? instantaneous**answer**5. Give one advantage of using an electronic timer rather than a hand held stopwatch. Removes effect of reaction time**answer**6. What is meant by the term acceleration? Change in speed per second**answer**7. Acceleration is measured in metres per second per second. Write this in symbol form. m/s/s or m/s2or ms-2**answer**8. What equation is used to find acceleration? a = (v-u)/t**answer**9. An object starts from rest and reaches 8m/s after 4s .Find the acceleration. a = (v-u) / t = (8-0)/4 2 m/s2**answer**The times for 4 cars to reach 100 km/h are shown below. Which car has the greatest acceleration? Car B (shortest time to go from 0 – 100 km/h)**answer**Speed time o 11. Describe the motion of the object represented by the speed – time graph below. Constant Speed**answer**A speed B time O 12. The velocity – time graphs for two objects are shown belowWhich object has the larger acceleration. Object A – steepest slope**answer**13. What is represented by the area under a speed- time graph? Distance travelled**answer**14. State three effects of a force. Change of speed, shape and direction.**answer**15. What is the unit of Force? Newtons (N)**answer**16. Name an instrument which can be used to measure forces. Newton balance or spring balance.**answer**17. What is a Scalar Quantity? Give examples. Scalar quantities can be described completely by their size or magnitude. e.g. Distance, time, mass and speed**answer**18. What is a vector? Give examples. Vectors are quantities with a magnitude and a direction. e.g. Weight, displacement, accelerationand velocity.**answer**19. What is the difference between speed and velocity. Velocity = displacement/time (vector) Speed = distance / time (scalar)**answer**20. Which force always opposes the motion of an object? Friction**answer**50N F 21.The forces on the object below are balanced. 50N**answer**22. The forces on an object are balanced.Describe the possible motion of the object. Stays at rest or moves with constant speed in a straight line.**answer**23. An unbalanced force causes an object to accelerate.What will affect the size of the acceleration? The size of the unbalanced force and the mass of the object**answer**400m 300m 300m 400m 24. A dog runs 300m south then turns and runs a further 400m east in a total time of 50s. What is the dog’s displacement from its starting position and its average velocity?. We use SOH CAH TOA to work out angle x° which we need to give the direction. tan X = 400/300 x° = tan-1 (400/300) x° = 53.1° This is the resultant displacement, the magnitude can be calculated by Pythagoras. S = √(3002 + 4002) S = 500m**answer**25. A 4kg object has an acceleration of 5m/s2.Find the unbalanced force acting on the object. F = m x a = 4 x 5 = 20N**answer**20N 10kg 26. Find the acceleration of the object shown below. 2m/s2

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