Forces and Motion

Question 1

Define scalar quantity and give 2 examples

Answer 1

It is a magnitude and it can be described fully with a single numerical value.
Ex: distance, speed, time, energy…

Question 2

Define vector quantity and give 2 examples

Answer 2

Has both magnitude and direction.
Ex: Force, velocity, displacement, moment…

Question 3

Which property of a distance-time graph can be used to calculate speed?

Answer 3

The gradient.

Question 4

Equation linking distance, time and speed with units.

Answer 4

speed(m/s)=d(m)/t(s)
d/v x t

Question 5

What is meant by acceleration? Give its unit.

Answer 5

Acceleration is the change in velocity per unit of time. (m/s²)

Question 6

State an equation linking acceleration, change in velocity and time taken.

Answer 6

Acceleration=(change in velocity)/time
a=(v-u)/t
v-u/a x t
v:final velocity u:initial velocity

Question 7

Which property of a velocity-time graph can be used to calculate acceleration?

Answer 7

Gradient

Question 8

Which property of a velocity-time graph can be used to calculate distance travelled?

Answer 8

Area under the graph

Question 9

State an equation linking final speed, initial speed, acceleration and distance travelled.

Answer 9

v²=u²+2as

Question 10

Name 2 types of forces that always oppose motion

Answer 10

1. Friction
   2.Air resistance

Question 11

Which type of force holds electrons around nucleus?

Answer 11

Electrostatic Force.

Question 12

State the ways a force can affect the body that is being applied on.

Answer 12

-Shape of the object.
-Speed
-Direction

Question 13

State an equation linking unbalanced force, mass and acceleration.

Answer 13

Force (N) =Mass (kg) x Acceleration (m/s²)
F= m x a

Question 14

State an equation linking mass, weight and gravitational acceleration

Answer 14

Weight (N) = Mass (kg) x g(m/s²)
W=m x g

Question 15

What is the relationship between stopping distance, breaking distance and thinking distance of a car whilst stopping?

Answer 15

Stopping dist=Thinking dist + Breaking dist

Question 16

State 7 factors that affect the stopping distance of a car

Answer 16

-Reaction time
-Initial speed
-Road conditions
-Tire conditions
-Weather conditions
-Driver’s conditions
-Mass of the car.

Question 17

2 factors that affect the air resistance acting on a falling object.

Answer 17

-Surface area
-Speed

Question 18

Describe how a falling object reaches to terminal velocity.

Answer 18

-First, the object falls under the effect of its weight accelerating with gravity
-As it accelerates air resistance opposing the motion increases and since F=ma acceleration decreases.
-When air resistance becomes equal to weight, forces are balanced so resultant force=0 thereforce a=0 and object reaches terminal velocity.

Question 19

State what is meant by obeying Hooke’s law

Answer 19

Extension is directly proportional with the force applied

Question 20

Explain the difference between elastic and plastic behaviour.

Answer 20

Elastic behaviour: Object recovers its original shape when the forces causing the extension is removed.
Plastic behaviour: There is a permanent deformation to the shape of the object when forces are removed.

Question 21

State an equation linking mass, velocity and momentum

Answer 21

P= m x v
Momentum (kgxm/s)=Mass (kg) x velocity (m/s)

Question 22

Explain what is meant by conservation of momentum

Answer 22

Total momentum before a collision (or explosion) is equal to total momentum after the collision (or explosion)

Question 23

State an equation linking force, change in momentum and time

Answer 23

Force= change in momentum/time taken
F= mv-mu/t
F=ΔP/t

Question 24

Explain how safety features such as seatbelt, crumple zone and airbags reduce risk of injury in accident

Answer 24

All of these safety features increases the stopping time during a collation by applying a force for longer period of time. Since ΔP=FxT and ΔP is constant, as stopping time increases, force applied on the driver decreases therefore the risk of injury decreases.

Question 25

Explain what Newton’s third law of physics states about forces

Answer 25

Newton’s third law states “for every action, there is an equal but opposite reaction.” This means all forces comes in pairs. Within these pars two forces have equal size but they act on different bodies in opposite direction.

Question 26

What is the centre of gravity?

Answer 26

Point where all the weight of the object acts
For uniform objects, its in the middle point of the object
As centre of gravity gets lower, stability increases.

Question 27

a) What is meant by moment?
b)When does it occur?
c)Is it scalar or vector?

Answer 27

a) Turning effect of the force
b) It occurs when a force applied away from the pivot (turning point), of the object perpendicularly
c) It is a vector quantity. It can be clockwise or anticlockwise

Question 28

How do you calculate the moment of a force?

Answer 28

Moment= Force x Perpendicular distance from pivot
The direction is referred to as either clockwise or anticlockwise

Question 29

State two conditions for an object to be considered in equilibrium

Answer 29

-Forces must be balanced (no resultant force)
-Clockwise moment = Anticlockwise moment