Topic 2 (again) Mechanics

Question 1

What is a scalar quantity?

Answer 1

Quantity with magnitude only, no direction

Question 2

What is a vector quantity?

Answer 2

A quantity with magnitude and direction

Question 3

What are the two methods to find the resultant vector?

Answer 3

• Trigonometry
• Scale diagram

Question 4

Define speed.

Answer 4

how far something is moving, regardless of direction

Question 5

Define displacement.

Answer 5

How far an object has traveled from its starting position

Question 6

define velocity.

Answer 6

The rate of change of an objects displacement

Question 7

what is instantaneous speed?

Answer 7

the speed of an object at any given time

Question 8

what must suvat equations have for them to work?

Answer 8

constant acceleration

Question 9

what is the force on an object due to gravity called?

Answer 9

weight

Question 10

what is g?

Answer 10

gravitational field strength / acceleration due to gravity and its equal to 9.81

Question 11

How do you calculate projectile motion of objects?

Answer 11

Resolve the initial velocity into horizontal and vertical components

Question 12

Why would videoing a projectile be useful?

Answer 12

• You can plot its course by recording its position in each frame
• You can work out the velocity if you know the frame rate

Question 13

Name a method of invesitgating projectiles?

Answer 13

Strobe photography, needs a reference object

Question 14

What can you learn from a displacement-time graph?

Answer 14

• The gradient is the velocity
• If you have a curve, the object is accelerating

Question 15

How do you find instantaneous velocity from a displacement-time graph?

Answer 15

Draw a tangent to the curve at the given time then calculate the gradient of the tangent

Question 16

What can you learn from a velocity-time graph?

Answer 16

• The gradient is the acceleration
• Area under the graph is the displacement

Question 17

What are free-body diagrams?

Answer 17

Diagrams that show all the forces acting on a body

Question 18

How can you find the resultant force if two forces are acting on an object?

Answer 18

Draw them “tip-to-tail” and then use trigonometry to calculate the angle and length

Question 19

What does newtons first law say?

Answer 19

if there is no resultant force on an object, the object will remain at constant velocity or rest (the velocity will not change)

Question 20

What does newtons second law state?

Answer 20

If there is a resultant force acting on an object, the object will accelerate.
This acceleration is proportional to the magnitude of the force
F = ma

Question 21

What does newtons third law say?

Answer 21

Each force has an equal and opposite reaction force

Question 22

Explain newtons third law

Answer 22

If object A exerts a force on B, then B will exert an equal but opposite force on A

Question 23

Define friction

Answer 23

A force that opposes motion

Question 24

What direction do frictional forces always act in?

Answer 24

in the opposite direction to the motion of an object

Question 25

What do frictional forces always do?

Answer 25

• slow something down
• convert kinetic energy into heat or sound

Question 26

What conditions does there need to be for an object to reach terminal velocity?

Answer 26

• A driving force that stays the same
• A frictional force that increases with velocity

Question 27

Why might a skydiver reach multiple terminal velocities in the same jump?

Answer 27

• Reaches one without parachute open
• Open parachute and then reaches another, just a far slower terminal velocity

Question 28

How do you calculate momentum?

Answer 28

momentum = mass x velocity

Question 29

What is always true about momentum?

Answer 29

• It is always conserved

Question 30

What units is momentum measured in?

Answer 30

kgms^-1

Question 31

If you divide momentum by time, what do you get?

Answer 31

Force

Question 32

Define work done,

Answer 32

Energy transferred

Question 33

how do you calculate work done?

Answer 33

W=fx
Work done = force x distance moved

Question 34

How is work done different to total energy?

Answer 34

Its just the energy transferred, doesnt include all the energy that stays in their stores

Question 35

What must be true about the direction to use w=fs?

Answer 35

The direction of the force is the same as the direction of motion

Question 36

define power.

Answer 36

the rate of doing work

Question 37

How do you calculate power?

Answer 37

Power = work done / time
P=w/t

Question 38

What is the conservation of energy?

Answer 38

Energy cant be created or destroyed, only transferred

Question 39

how do you calculate kinetic energy?

Answer 39

Ek = 1/2 m v^2

Question 40

How is GPE calculated?

Answer 40

mgh
mass x gravitational field strength x height

Question 41

how is energy “lost”?

Answer 41

it is dissipated to useless energy stores

Question 42

What is efficiency?

Answer 42

How well a device converts the energy put in into useful energy out

Question 43

How do you calculate effiiciency?

Answer 43

Useful energy input / total energy output x 100

Can be power instead of energy

Question 44

Define mass

Answer 44

The amount of matter an object has

Question 45

How do you calculate weight?

Answer 45

w = mg
mass x gravitational field strength

Question 46

Define centre of gravity?

Answer 46

The single point through which an object’s weight can be considered to act

Question 47

What is a moment?

Answer 47

The turning affect of a force

Question 48

How do you calculate a moment?

Answer 48

M = Fx
Force x Perpendicular distance from pivot

Question 49

What must be true for an object to be in equlibrium?

Answer 49

• Forces must be balanced
• net moment must be zero