Mechanics

Question 1

2.1.1 Define displacement, velocity, speed and acceleration

Answer 1

Displacement: The vector quantity from a given fixed point to the position of another point.
Velocity: The ratio of the change of displacement to the time taken. - A vector.
Speed: The ratio of the distance covered to the time taken to cover the distance. - A scalar.
Acceleration: Change of velocity over time. Instantanous = the rate of change with time of the velocity. - A vector.

Question 2

2.1.2 Explain the difference between instantaneous and average values of speed, velocity and acceleration.

Answer 2

Average speed: Ratio of TOTAL distane travelled to the TOTAL time taken.
Instantaneous: Ratio of distance travelled in an instant.
Average velocity: Ratio of change of displacement to the time taken.
Instantaneous: Velocity in one particular instant.
Average Acceleration: Ratio of change of velocity to the time taken.
Instantaneous: Acceleration in an instant.The rate of change with time of the velocity vector.

Question 3

2.1.3 Outline the conditions under
which the equations for uniformly
accelerated motion may be applied.

Answer 3

Motion on a straght line and constant acceleration

Equations: 
v = u + at
s = ((u+v)/2)t
v^2 = u^2 + 2as
s = ut + 1/2at^2
s = vt - 1/2at^2

Question 4

2.1.4 Identify the acceleration of a body
falling in a vacuum near the Earth’s
surface with the acceleration g of free
fall.

Answer 4

9.81 ms^-2 (ignoring air-resistance)

Question 5

2.1.5 Solve problems involving the equations of uniformly accelerated motion

Answer 5

GO DO EXAM PROBLEMS OR SOMETHING

Question 6

2.1.6 Describe the effects of air resistance

on falling objects.

Answer 6

The air resistance is directly proportional to the velocity of the object. Terminal velocity is when the air resistance is equal to the actual acceleration caused by gravity, causing the object to have no net acceleration. The shape and the mass of an object also affects the drag forced.
You are often asked to draw two projectiles where one is affected by air resistance and the other is not. When it is a vertical projectile, the object with air resistance will simply not go up as high. If it is horizontal, it object with air resistance will land at a point closer to the original object. If it is launched at an angle, then you combine both of the previous ones to determine the projectile of the object with air resistance, i.e. it will not go up as high, and will not travel as far.

Question 7

2.1.7 Draw and analyse distance–time
graphs, displacement–time
graphs, velocity–time graphs and
acceleration–time graphs.

Answer 7

When drawing these graphs, simply plot the data given to you. Time always goes on the x-axis and the other goes on the y-axis.

Question 8

2.1.8 Calculate and interpret the gradients
of displacement–time graphs and
velocity–time graphs, and the areas
under velocity–time graphs and
acceleration–time graphs.

Answer 8

-Slope of displacement - time graphs gives the velocity
- Slope of velocity - time graphs gives the acceleration
- Area under velocity - time graph gives the change in displacement
- Area under acceleration - time graphs gives the change in velocity
NOW DO EXAM QUESTIONS ON THIS

Question 9

2.1.9 Determine relative velocity in one and

in two dimensions.

Answer 9

All velocity is relative to your frame of refrence. If you’re walking at the speed va = 1 km/h and a car drives past you at vb= 30 km/h, the velocity of the car with respect to you is:
v = vb - va
v = (30 - 1) km/h = 29km/h

The relative velocity is the net velocity. Recall that velocity is the speed in a given direction. Therefore, in one dimension you have to determine in which direction the object is travelling and you must use the ratio between the displacement and time and not the ratio between speed and time. In two dimensions, you have to know the angle between the direction the object is travelling in, and the axis of the direction you are required to calculate the velocity in. You then multiply the speed of the object with the cosine of the angle to determine the velocity.

Question 10

2.2.1 Calculate the weight of a body using

the expression W = mg.

Answer 10

W = mg You can do that, believe me you can

Question 11

2.2.2 Identify the forces acting on an
object and draw free-body diagrams
representing the forces acting.

Answer 11

Each force should be labelled by name or given
a commonly accepted symbol. Vectors should
have lengths approximately proportional to their
magnitudes. See sub-topic 1.3. Do some tasks on this.

Question 12

2.2.3 Determine the resultant force in

different situations.

Answer 12

Net force is the single force whose effect is the same as the combined effect of all individual forces on the body. This is found by vector addition. The resultant of two forces can be maximum the two added (they are both working in the same direction), and minimum the two subtracted from each other (they work in opposite directions)

Question 13

2.2.4 State Newton’s first law of motion.

Answer 13

When the resultant force on a body is zero, its velocity is constant ie: it will either stand still or move with constant velocity.

Question 14

2.2.5 Describe examples of Newton’s first

law.

Answer 14

A book lying on table. Anything with constant velocity really.

Question 15

2.2.6 State the condition for translational

equilibrium.

Answer 15

Equilibrium: the situation when the sum of forces on a body is zero. If an object is at rest, then it is in static equilibrium and, if it is moving with constant velocity, then it is in dynamic equilibrium

Question 16

2.2.7 Solve problems involving translational

equilibrium

Answer 16

Well go find some problems to solve, my love.The ones with threads and bodys hanging in angles and stuff are cool.

Question 17

2.2.8 State Newton’s second law of motion.

Answer 17

F=ma. The net force acting on an object (of constant mass) is the product of the objects’ mass and the net acceleration of the object. It can also be written as Delta p/ delta t Figure out why

Question 18

2.2.9 Solve problems involving Newton’s

second law.

Answer 18

F = ma
How to solve a mechanics problem:
- Draw a free-body fiagram showing all forces acting on each body
- Find net force for each body
- Use Newton’s second law separately on each body, or treat all the bodies as one if convenient.
NB You should check out those two bodies connected with a string problems

Question 19

2.2.10 Define linear momentum and impulse

Answer 19

Momentum: p = mv HERE’S THE EXPLANATION FOR THE Delta p mentioned above!!!
The product of the mass and velocity of a body, a vector with the same direction a s the velocity.
Impulse: The average force on a body multiplied with the time for which the force was acting. It is the area of a graph of F against t.

Question 20

2.2.11 Determine the impulse due to a
time-varying force by interpreting a
force–time graph.

Answer 20

Impulse: The average force on a body multiplied with the time for which the force was acting. It is the area of a graph of force against time.

Question 21

2.2.12 State the law of conservation of linear

momentum.

Answer 21

If the total external force acting on a system is zero then the momentum of the system remains constant.

Question 22

2.2.13 Solve problems involving momentum

and impulse.

Answer 22

You always know that the total momentum before and after an event is the same if there is no external force acting on the system. By using this you can create an expression to determine certain unknown values.

Question 23

2.2.14 State Newton’s third law of motion.

Answer 23

If body A exerts a force on body B, then B will exert an equal and opposite force on A.

Question 24

2.2.15 Discuss examples of Newton’s third

law.

Answer 24

Check out the inclined plane problems (think you might get some of those).

Question 25

2.3.1 Outline what is meant by work.

Answer 25

Work is the process of converting energy. It is equal to the product of the force applied and the distance it has moved. W = F * s Unit: Joules, J

Question 26

2.3.2 Determine the work done by a
non-constant force by interpreting a
force–displacement graph.

Answer 26

A typical example would be calculating the work
done in extending a spring
The area below a Force-displacement graph is equal to the work done.

Question 27

2.3.3 Solve problems involving the work

done by a force.

Answer 27

just do problems here tooooo

Question 28

2.3.4 Outline what is meant by kinetic

energy

Answer 28

The energy of a moving body because of its movement. Ek = 1/2 mv^2 Unit: Joules

Question 29

2.3.5 Outline what is meant by change in

gravitational potential energy.

Answer 29

Gravitational potential energy is energy that is stored in an object by its height. ∆Egravp = mg∆h
Unit: Joules

Question 30

2.3.6 State the principle of conservation of

energy.

Answer 30

Energy is conserved; this means that the total amount of energy in the universe is constant.
Energy cannot be made or destroyed. It can be transformed from one form to another.

Question 31

2.3.7 List different forms of energy
and describe examples of the
transformation of energy from one
form to another.

Answer 31

Gravitational potential, kinetic energy, thermal energy, electrostatic potential energy, chemical energy.

Object falls. Grav pot –> kin en –> thermal en (when it hits the ground)

Question 32

2.3.8 Distinguish between elastic and

inelastic collisions.

Answer 32

An elastic collision is a collision where no mechanical energy is lost. For elastic collisions the relative velocity before is always equal to the relative velocity after
the collision.
Most collisions are inelastic because kinetic energy is transferred to other forms of energy—
such as thermal energy, potential energy, and sound—during the collision process. If you are
asked to determine if a collision is elastic or inelastic, calculate the kinetic energy of the
bodies before and after the collision. If kinetic energy is not conserved, then the collision is
inelastic.

Question 33

2.3.9 Define power.

Answer 33

Power is the rate of doing work or transferring energy.
Power is work done over time. The unit of power is the Watt (W). 1 watt is equivalent to 1 Joule of energy being
transformed per second.

Question 34

2.3.10 Define and apply the concept of

efficiency.

Answer 34

In any energy transfer some of the work is transferred into a form that is not useful. This
energy is wasted. Efficiency is defined as the ratio of the useful energy to the total energy
transferred.
Efficiency = Useful energy out/Total energy in
Expressed as a percentage.

Question 35

2.3.11 Solve problems involving momentum,

work, energy and power.

Answer 35

meeeeeeeeep do stuff (I love you)

Question 36

2.4.1 Draw a vector diagram to illustrate
that the acceleration of a particle
moving with constant speed in a
circle is directed towards the centre of
the circle.

Answer 36

illustrate that the acceleration of a particle
moving with constant speed in a
circle is directed towards the centre of
the circle.

Question 37

2.4.2 Apply the expression for centripetal

acceleration.

Answer 37

Acceleration = v^2/r

Question 38

2.4.3 Identify the force producing circular

motion in various situations

Answer 38

The only force on the Moon in its orbit is the pull of the Earth, which supplies the centripetal
force. Friction acts sideways on the tyres of a
car turning a corner. Tension of a string when swinging something around.

Question 39

2.4.4 Solve problems involving circular

motion.

Answer 39

Do probs <3