Physics Mechanics

Newton's First: Force=change in momentum/time taken for change

• P before = P after 
• P=Fxt where t is impulse (the area under an F by t graph
  

• Momentum is a vector
• Elastic collisions are when Kinetic energy is conserved but when Kinetic energy is lost, the collision is Inelastic
• Elastic collisions are given by: 
  v^2=u^2+x^2 (x=2as) 
• The Scale diagram will form a right angled triangle

The centre of Gravity is the point through which gravity acts
and is the point where the mass of the body seems to be concentrated

Stability is when (stable equilibrium):

The centre of gravity acts              The Centre of gravity acts through the through the bottom of the base    pivoting point

Instability is when (unstable equilibrium):

The C of G acts within the base     The C of G acts outside the base
the body rolls onto base                 the body rolls onto side

Or raising the C of G in the situation of gravity acting through pivot point as the line of action lies outside the base, it becomes unstable and so toples over. This is like over loading the roof rack of a car.

Force diagrams can be solved by taking measurments on a to scale diagram or by using triganometry if the forces create a right angled traingle or pythagorus.

Efficiency

Work done=weight x height gain         Efficiency=Useful energy out /
                                                                 total energy in

A 1kw motor is 10% efficient. How much mass could it lift, through a height of 5m, in 2 minutes?                  Assume g=10N/Kg

1Kw=1000W    10% efficiency means 1000 x 10/100=100W
so Energy=power x time = 100 x (2 x 60) =12000J
E=mgh => 12000=m x 10 x 5 => 12000= m x 50 so m=12000/50 = 240Kg

Newton's first:        An object at rest will remain stationary or will continue to move at constant speed or velocity unless acted on by an unbalanced force.

Newtons's second: Acceleration is produced when a force acts on a body.The greater the mass, the greater the force is needed tocause an acceleration or decelaration

Newton's Thirds:    For every force exerted there is an equal and opposite force reaction

Displacement time graphs: Gradient = vilocity
Vilocity rime graphs: Gradient=Acceleration and Area underneath = displacement
Horizontal straight line on vt graph means constant speed, Straight diagonal line on vt graph means constant acceleration

Work done(Nm/J) = Force x distance moved in the direction of force

A ball held up in the air, has potential energy unless release and this then becomes kinetic energy
Ep = mgh

As well as gravitational potential energy, energy may also be stored chemically, elastically, magnetically or as strain energy

Ek = 1/2mv^2            Energy transfered as heat = mass x temp
                              change x specific heat capacity

Power (or rate at which energy is transfered) = energy transfered / time

v =Final velovity (m/s)       t = time (s)      u = initial velocity (m/s)
a = acceleration (m/s^-2)        s = distance (m)

v = u + at                     s = (v + u)t / 2
v^2 = u^2 + 2as             s = ut + at^2 / 2

A mass of 10Kg is raised 5m in i minute. What is it's gain in potential energy? What is the power?

Ep = mgh = 10 x 9.81 x 5 = 490J
Power = W/t = 490 / 60 = 8.17W

A canon is shot at 100m/s at 30 degrees to the horizontal.
1) H = 100cos30 and V = 100sin30 so time of flight:
v = u + at so 0 = 50 + -10t so t = 5s so time of flight = 10 seconds
2) Range = horizontal velocity x time of flight = 86.7 x 10 = 867m

diastance = average velovity x time
acceleration = (v-u)/t