Forces & Motion

Question 1

What is the unit of force

Answer 1

Newtons

Question 2

Equation: Average speed =

Answer 2

Average speed = distance / time

Question 3

Equation: Speed =

Answer 3

Speed = distance/time

Question 4

Equation: Acceleration =

Answer 4

Acceleration = change in velocity/time
a = v-u / t

Question 5

gradient of a Distance time graph =

Answer 5

speed

Question 6

Gradient of a velocity time graph =

Answer 6

acceleration

Question 7

Area under a velocity time graph =

Answer 7

distance travelled

Question 8

What piece of equipment do you use to measure the speed of an object?

Answer 8

a light gate and data logger linked to a computer

Calculates velocity for you

Question 9

What are the 3 effects of forces?

Answer 9

Forces can:
change shape
change speed
change direction

Question 10

What is the difference between a scalar quantity and a vector quantity?

Answer 10

Scalars have size only (eg mass, temp, speed)
Vectors have size and direction (eg force, acceleration, velocity)

Question 11

If a 6N force acts up on an object and a 10N force acts down, what is the resultant (unbalanced) force?

Answer 11

10 - 6 = 4N down
(remember always say direction as force is a vector)

Question 12

Equation: Resultant Force F =

Answer 12

Resultant F=ma

Question 13

Equation: Weight W =

Answer 13

W = mg

Question 14

Equation: Stopping distance =

Answer 14

Stopping distance = Thinking distance + Braking distance

Question 15

Factors affecting thinking distance are:

Answer 15

Speed
Increased reaction time caused by:
distractions
drugs/alcohol
visibility

Question 16

Factors affecting braking distance:

Answer 16

Speed
Mass
Wet/slippery road
Worn tyres and brakes

Question 17

Describe the motion of a falling object (eg a skydiver)

Answer 17

At start, weight force great than air resistance
This unbalanced force causes acceleration
As speed increases, air resistance increases
But weight stays the same
So Unbalanced force decreases so does acceleration
Until Weight = air resistance
Terminal velocity is reached

Question 18

What is the force that always opposes motion?

Answer 18

Friction

Question 19

What is the force between two magnets?

Answer 19

Magnetic force

Question 20

What is the force between two charges?

Answer 20

Electrostatic force

Question 21

What is the force in a stretched rope?

Answer 21

Tension force

Question 22

What is the force acting up on a wing of a bird or plane?

Answer 22

Lift force

Question 23

What is the force pulling an object towards the earth?

Answer 23

Gravitational (also called weight)

Question 24

What is the force acting upwards on a floating object?

Answer 24

Upthrust

Question 25

What is the force acting against a moving car?

Answer 25

Air resistance (also called drag)

Question 26

What is the force acting against a moving fish?

Answer 26

Drag

Question 27

Moment of a force =

Answer 27

Force x perpendicular distance force to pivot

Question 28

Force on a spring or wire
F =

Answer 28

F = kx

x is extension
k is spring constant

Question 29

What features of a load vs extension graph tells you the spring obeys Hookes Law?

Answer 29

Straight line graph through the origin

Question 30

Describe elastic behaviour

Answer 30

Ability of a material to return to original shape when extending force is removed

Question 31

What is centre of gravity?

Answer 31

Point through which all the weight appears to act

Question 32

What is the Principle of moments?

Answer 32

In equilibrium,
Total moment clockwise = Total moment anti-clockwise

Question 33

Hooked law states….

Answer 33

Extension is directly proportional to load
Load force F = kx

Question 34

How can you tell by looking at the force extension graph for a stretched wire that it obeys Hooke’s Law

Answer 34

straight line through the origin
F = kx extension is directly proportional to load

Question 35

Describe an experiment to investigate how extension varies with load on a spring, wire or rubber band.

Answer 35

What - measure the original length
With - a metre rule
How - Avoid parallax by having spring and ruler close together (how to measure)
Add weight
Measure new length
Calculate extension = new length - original
Add another weight
Continue until you have a good range of readings.
Repeat by unlaoding and measuring extension.

Question 36

Eqn of motion v2 =

Answer 36

v2 = u2 + 2as

Question 37

Momentum p =

Answer 37

momentum = mass x velocity
p = mv

Question 38

Principle of conservation of momentum

Answer 38

in a collision or explosion
total momentum before = total momentum after

Question 39

Equation linking force and momentum

Answer 39

Force = change in momentum/time

F = m (v-u) / t

Question 40

Impulse = change in momentum
Impulse =

Answer 40

impulse = force x time
Impulse = Fxt

Question 41

How to safety features such as set belts and air bags reduce risk of injury?

Answer 41

They increase the time to change the momentum of the passenger.
As Force = change in momentum/time,
time increases to change momentum so force is reduced.
Less injury.

Question 42

State Newton’s Third Law

Answer 42

If object A exerts a force on object B
then object B exerts an equal and oppostie force on object A

Question 43

What is true about Newton Third Law pairs of forces

Answer 43

Same size
Opposite direction
Same type of force
Act on different objects