Mechanics

Question 1

What is a moment ?

Answer 1

It is the turning effect of a force. The force multiplied by the perpendicular distance between the line of action of the force and the pivot

Question 2

What does the principle of moments state ?

Answer 2

For an object in equilibrium the sum of clockwise moments is equal to the sum of the anticlockwise moments about the same point

Question 3

What is a couple ?

Answer 3

A pair of force of equal size which acts parallel to each other but in opposite directions. They produce a turning force called moment of a couple / torque

Question 4

How do you calculate the torque ?

Answer 4

The force multiplied by the perpendicular distance between the two forces

Question 5

What is the centre of mass ?

Answer 5

The point where the entire mass of an object is assumed to be concentrated

Question 6

What is the centre of gravity ?

Answer 6

The point at which all the weight is assumed to be acting

Question 7

How can you find the centre of mass of irregular objects ?

Answer 7

The intersection of the lines of symmetry

Question 8

How to you find the centre of mass of an irregular object ?

Answer 8

If the object is suspended and release the centre of mass would be directly below the point of suspension ( plumb line - used to draw the path )

Multiple lines - intersection = point of centre of mass

Question 9

When is an object said to be stable ?

Answer 9

If it returns to its original position when disturbed.

Question 10

What are the factors of stability ?

Answer 10

The width of the base - the wider the width the more stable you are
The lower the centre of mass - the more stable the object is

Question 11

How does terminal velocity occur ?

Answer 11

• when an object is dropped its only component making it accelerate is the weight . Over time the air resistance increases as the speed increases until it is equal to the weight the object has now resultant force acting on it reaches terminal velocity.

Question 12

What is Newton’s first law ?

Answer 12

An object remains at constant motion or rest unless acted upon by a resultant force which causes the object to accelerate

Question 13

What is inertia ?

Answer 13

The tendency of a body to resist any change in its motion (speed or direction )

Question 14

What does Newton’s second law state ?

Answer 14

If an unbalanced force acts upon an object then the object will accelerate in the direction of the resultant force and is inversely proportional to the mass of the object

Question 15

What does Newton’s third law state ?

Answer 15

If object a exerts a force on object b then object b must exert an equal and opposite force back on the object a

Question 16

How does having a greater width and a lower centre of mass mean a greater stability ?

Answer 16

The line of action (weight) more likely to act within the base of the object - stable and can return back to its original position

Question 17

What is meant by distance ?

Answer 17

Refers to how far an object travels

Question 18

What is meant by displacement ?

Answer 18

Refers to the distance travelled in a particular direction ( from point a to b - shortest distance )

Question 19

What is meant by speed ?

Answer 19

The rate of change of distance ( distance travelled per unit time )

Question 20

What is meant by velocity ?

Answer 20

Velocity is the rate of change of displacement ( displacement per unit time )

Question 21

What does a straight slope on a displacement time graph tell us ?

Answer 21

That the object is travelling at a constant speed

Question 22

What does a straight horizontal line on a displacement time graph tell us ?

Answer 22

The object is stationary - not moving

Question 23

What does a curved slope on a displacement time graph tell us ?

Answer 23

The object is accelerating

Question 24

What does the gradient of a displacement time graph give us ?

Question 25

What does the gradient of a displacement time graph give us ?

Answer 25

The velocity

Question 26

What does a straight slope on a velocity time graph represent ?

Answer 26

The object is accelerating at a constant rate

Question 27

What does a horizontal line on a velocity time graph tell us ?

Answer 27

- constant speed

Question 28

What does the area under a velocity time graph give ?

Answer 28

Distance travelled

Question 29

What does the gradient of a velocity time graph give ?

Answer 29

The acceleration of the object

Question 30

Why does an object thrown and dropped both reach the ground at the same time ?

Answer 30

- the only force acting on the objects is gravity, acting on the vertical direction - the horizontal motion is unaffected as there is no resulting force that causes the object to accelerate in the horizontal direction

Question 31

Rules for projectile motion ?

Answer 31

- horizontal and vertical must be treated separately - gravity only acts in the vertical direction - horizontal component = no acceleration so constant velocity - vertical acceleration is 9.81 due to gravity

Question 32

How would you find the velocity at a point in projectile motion ?

Answer 32

Using the vertical and horizontal velocity at the point and using Pythagorus

Question 33

What is momentum ?

Answer 33

Momentum is the product of an object’s mass multiplied by the velocity

Question 34

Was is the unit of measure for momentum?

Answer 34

Ns or Kgms^-1

Question 35

How can the momentum be linked to Newton’s second law ?

Answer 35

F= m*a = m (v-u ) / t Rate of change of momentum of a body is directly proportional to the external force acting on the body

Question 36

What is impulse ?

Answer 36

Defined as the product of the force and the time ( change in momentum)

Question 37

What are the units for impulse ?

Answer 37

Ns

Question 38

How can you decrease the force/ impact on an object ?

Answer 38

- increase the time taken to produce the change in momentum

Question 39

Examples of car Saftey features to reduce the force/ impact ?

Answer 39

- seatbelts / crumple zones / airbags These increase the time taken for the change in momentum reducing the force that the person would feel

Question 40

What does the law of conservation of momentum state ?

Answer 40

Provided that there are no external forces acting on the system , the total momentum of a system is always conserved

Question 41

What are elastic collisions ?

Answer 41

Collisions when the momentum and the kinetic energy is conserved - no energy is dissipated into the surroundings

Question 42

What are inealstic collisions ?

Answer 42

Collisions when the momentum is conserved but not the kinetic energy - kinetic energy is transferred into other forms of energy

Question 43

Define work

Answer 43

The product of the force and the distance moved in the direction of the force

Question 44

How can you work out the work done using a force displacement graph ?

Answer 44

- the area under

Question 45

Define power

Answer 45

The rate at which energy is transferred/ work done

Question 46

What is the unit for power ?

Answer 46

Watts

Question 47

Define 1 watt ?

Answer 47

The work done at the rate of 1 joule per second

Question 48

What is the relation ship between the power and the force ?

Answer 48

P = Fv

Question 49

Define energy ?

Answer 49

The ability of a body to do work. When work is done, energy is transferred

Question 50

What does the law of conservation of energy state ?

Answer 50

Energy can neither be destroyed or created, can only be transferred from one form to another - total energy is constant

Question 51

What is efficiency ?

Answer 51

The proportion of energy that is usefully transferred. The smaller the amount of wasted energy, the greater the efficiency

Question 52

When can F = ma not be used ?

Answer 52

When the mass isn’t constant

Question 53

What happens to the acceleration if the velocity increases?

Answer 53

There would be a greater acceleration

Question 54

What is meant by the net force ?

Answer 54

The combined effect of all the forces on an object

Question 55

Define linear momentum

Answer 55

Product of the mass and the velocity

Question 56

Examples of scalars ?

Answer 56

- temperature , speed , distance , energy, mass

Question 57

Examples of a vector ?

Answer 57

- velocity , displacement , momentum, acceleration

Question 58

How would you work out the point of an instantaneous speed on a displacement time graph ?

Answer 58

- tangent to the point

Question 59

How would you work out if an elastic closing is conserved ?

Answer 59

U1 +v1 = u2 + V 2 Initial velocity + final velocity of particle a is equal to initial velocity + final velocity of particle b

Question 60

What are the forces you can have acting on an object ( free body diagram ) ?

Answer 60

Tension , Normal , weight , Ar, driving force , friction