1. S4 Physics Forces 2 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22

2. 1. State 3 possible effects of a force
answer
Change an objects
Shape
Speed
Direction

3. . 2.Define the gravitational field strength of a planet.
answer
The force of gravity acting on a mass of one kilogram.

4. 3. Write down a relationship between weight, gravitational field strength and mass.  
answer
Weight = mass x gravitational field strength

5. 4. An object is travelling at 2ms-1 when the forces on it become balanced. Describe how the object now moves.  
answer
The object continues to move in a straight line with a constant speed of 2ms-1

6. 5. An object of mass of 2kg has an acceleration of 3 ms-2
5. An object of mass of 2kg has an acceleration of 3 ms-2. What unbalanced force is acting on the object?  
answer
F = ma
F= 2 x 3
F = 6N

7. 6. A person transfers 50J of energy when pushing an object 2m along a bench. What was the force exerted?  
answer
EW = F x d
50 = F x 2
F = 25N

8. 7. A machine transfers 800J of energy in a time of 40 seconds
7. A machine transfers 800J of energy in a time of 40 seconds. Find the power output.
answer
P = E/t
P = 800/40
P = 20W

9. 8. State the equations which allow us to calculate kinetic and potential energy.  
answer
Potential Energy EP = mgh
Kinetic Energy EK = ½ mv2

10. 9. How much potential energy does a 5kg mass gain when it is lifted through 2m?  
answer
EP = mgh
EP = 5 x 9.8 x 2
EP = 98J

11. 10. An object of mass 3kg has a speed of 2ms-1
10. An object of mass 3kg has a speed of 2ms-1. Calculate its kinetic energy.  
answer
EK = ½ mv2
EK = ½ x 3 x 22
EK = 6J

12. All of the potential energy is converted to kinetic.
11. An object gains 100J of potential energy when it is lifted from the ground It is then dropped. Assuming no air resistance, what will be its kinetic energy when it hits the ground?  
answer
100J.
All of the potential energy is converted to kinetic.

13. 12. State the difference between scalars and vectors
answer
A scalar has magnitude (size) only but a vector has magnitude and direction.

14. SCALARS mass, time, energy, speed
13. Divide the following quantities into scalars and vectors.   Force, mass, time, weight, velocity, energy, speed, displacement
answer
SCALARS mass, time, energy, speed
VECTORS force, weight, velocity, displacement

15. 14. An object falls freely towards the earth. What is its acceleration?  
answer
9.8ms-2

16. The hot gases exert an upward force on the rocket. ( Newton’s 3rd Law)
15. When a rocket lifts off it pushes hot gases downwards. Why does the rocket move up?
answer
The hot gases exert an upward force on the rocket.
( Newton’s 3rd Law)

17. 16. A model rocket has a weight of 2N. It produces a thrust of 8N
16. A model rocket has a weight of 2N. It produces a thrust of 8N. What is the unbalanced force acting on the rocket?  
answer 6N

18. 17. Why does a projectile follow a curved path?
answer
A projectile has both a horizontal and vertical motion.
It moves across and down at the same time.

19. 18. Describe the horizontal and vertical motions of a projectile.
answer
HORIZONTAL constant speed
VERTICAL constant acceleration( 9.8ms-2 )

20. 19. A ball is fired from a platform.
State two ways of increasing the horizontal range.
answer
Increase the height of the platform.
Increase the horizontal speed of the cannonball.

21. 20. A ball is kicked off a roof with a horizontal speed of 7ms-1
20. A ball is kicked off a roof with a horizontal speed of 7ms-1 It hits the ground 2seconds later. How far from the is the roof when it lands?
answer
d = v x t
d = 7 x 2
d = 14m

22. a = (v-u)/t 9.8 = (v-0)/3 v = 29.4 ms-2 answer
21. An object is dropped from a tall building and hits the ground 3 seconds later. Find its speed on hitting the ground.
answer
a = (v-u)/t
9.8 = (v-0)/3
v = 29.4 ms-2

23. 22. How long does a geostationary satellite
22. How long does a geostationary satellite take to make one orbit of the earth?    
answer
24 hours