S3 Physics - Forces 1 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26

1. What two measurements are needed to calculate the average speed of an object? answer Distance and Time

2. What equation would be used to calculate average speed? answer Speed = distance / time

3. A trolley takes 1.5 s to travel 60cm Calculate its average speed. . answer v = d/t = 60 / 1.5 = 40 cm/s

4. Does a car speedometer give average or instantaneous speed? answer instantaneous

Removes effect of reaction time 5. Give one advantage of using an electronic timer rather than a hand held stopwatch. answer Removes effect of reaction time

6. What is meant by the term acceleration? answer Change in speed per second

7. Acceleration is measured in metres per second per second 7. Acceleration is measured in metres per second per second. Write this in symbol form. answer m/s/s or m/s2or ms-2

8. What equation is used to find acceleration? answer a = (v-u)/t

9. An object starts from rest and reaches 8m/s after 4s 9. An object starts from rest and reaches 8m/s after 4s . Find the acceleration. answer a = (v-u) / t = (8-0)/4 2 m/s2

(shortest time to go from 0 – 100 km/h) The times for 4 cars to reach 100 km/h are shown below. Which car has the greatest acceleration? answer Car B (shortest time to go from 0 – 100 km/h) Car Time(s) A 10.1 B 8.3 C 16.4 D 12.9

11. Describe the motion of the object represented by the speed – time graph below. Constant Speed answer

Object A – steepest slope 12. The velocity – time graphs for two objects are shown below Which object has the larger acceleration. A B time speed O answer Object A – steepest slope

13. What is represented by the area under a speed- time graph? answer Distance travelled

14. State three effects of a force. answer Change of speed, shape and direction.

15. What is the unit of Force? answer Newtons (N)

16. Name an instrument which can be used to measure forces. answer Newton balance or spring balance.

17. What is a Scalar Quantity? Give examples. answer Scalar quantities can be described completely by their size or magnitude. e.g. Distance, time, mass and speed

18. What is a vector? Give examples. answer Vectors are quantities with a magnitude and a direction. e.g. Weight, displacement, acceleration and velocity.

19. What is the difference between speed and velocity. answer Velocity = displacement/time (vector) Speed = distance / time (scalar)

20. Which force always opposes the motion of an object? answer Friction

21.The forces on the object below are balanced. answer 50N F 50N

Stays at rest or moves with constant speed in a straight line. 22. The forces on an object are balanced. Describe the possible motion of the object. answer Stays at rest or moves with constant speed in a straight line.

The size of the unbalanced force and the mass of the object 23. An unbalanced force causes an object to accelerate. What will affect the size of the acceleration? answer The size of the unbalanced force and the mass of the object

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?. answer 300m 400m 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

25. A 4kg object has an acceleration of 5m/s2 25. A 4kg object has an acceleration of 5m/s2. Find the unbalanced force acting on the object. answer F = m x a = 4 x 5 = 20N

26. Find the acceleration of the object shown below. answer 2m/s2 10kg 20N