Mechanics And Further Mechanics Flashcards
Acceleration
Is the vector defined as the rate of change of velocity
Average speed
Is calculated by dividing the total distance for a journey by total the time for the journey
Moment=Fx
Moment (Nm)
F=force (N)
x=perpendicular distance from pivot (m)
F=ma
W=mg
F=force (N)
m=mass (kg)
a=acceleration (m/s^2)
g=acceleration due to gravity (9.81 m/s^2)
GPE=mgh
KE=1/2mv^2
GPE=gravitational potential energy (J) KE=kinetic energy (J) m=mass (kg) g=acceleration due to gravity (9.81 m/s^2) h=change in height (m) v=velocity (m/s)
P=E/t
P=power (W)
E=energy (J)
t=time (s)
WD=Fs
WD=work done (J)
F=force (N)
s=displacement (m)
Efficiency=useful energy output/. total energy input x 100%
Efficiency=useful power output/total power input x 100%
p=mv
p=momentum (kgm/s)
m=mass (kg)
v=velocity (m/s)
F=p/t
F=force (N)
p=momentum (kgm/s)
t=time (s)
m1u1+m2u2=m1v1+m2v2
Total momentum before collision=total moment after collision
m=mass (kg)
u=initial velocity (m/s)
v=final velocity (m/s)
I=Ft
I=mv-mu
I=impulse (Ns)
F=force (N)
t=time (s)
Impulse=change in momentum
Ø=s/r
Ø=angle (radians)
s=length of arc (m)
r=radius (m)
Complete circle: s=2rpi
w=ø/t
w=angular velocity (rad/s)
t=time (s)
Full circle: 2pi/T
T=time period
f=1/T
f=frequency (Hz)
T=time period
v=rø/t
v=rw
v=instantaneous velocity (m/s)
w=angular velocity
r=radius (m)
F=(mv^2)/r
F=mrw^2
F=centripetal force M=mass (kg) v=instantaneous velocity (m/s) r=radius (m) w=angular velocity (m/s)
Centre of gravity
Is the point, on an object, through which the weight of an object appears to act.
Conservation of energy
Energy can never be created or destroyed
Conservation of linear momentum
The vector sum of the momenta of all objects in a system is the same before and after any interaction (collision) between objects.
Displacement
The vector measurement of a distance in a certain direction.
Displacement-time graph
Graph showing the positions visited on a journey, with displacement on y axis and time on x axis.
Gradient is velocity.
Efficiency
Effectiveness of a machine at converting energy usefully
Energy
Is the property of an object that gives it the capacity to do work.
Change in energy is the same as work being done
Equilibrium
A body is in equilibrium if there is zero resultant force and zero resultant momentum. It will have zero acceleration.
Explosion
Is it situation in which a stationary object (or system of joined objects)separates into component parts, which move off at different velocities. The momentum must be conserved in explosions
Free-body force diagram
A diagram with the object isolated and all the forces that act on it are drawn in at the points where they act, using arrows to represent the forces.
Instantaneous speed
Speed at any particular instant in time on a journey, which can be found from the gradient of the tangent to a distance-time graph at that time.
Kinematic
Study of the description of the motion of objects
Newton’s first law
An object will remain at rest, or in a state of uniform motion, until acted upon by a resultant force.
Newton’s third law
For every action, there is an equal and opposite reaction.
Power
Rate of energy transfer
Principles of moments
A body will be in equilibrium if the sum of clockwise moments acting to it is equal to the sum of the anti clockwise moment
Projectile
Moving object on which the only force is significance acting is gravity. The trajectory is thus pre-determined by its initial velocity.
Resultant force
Total force acting on a body when all the forces acting are added together accounting for their directions.
Scalar
Quantity that only has magnitude
Scalar
Tension
Is a force acting within a material in a direction that would extend the material
Terminal velocity
Velocity of a falling object when it’s weight is balanced by the sum of the drag and upthrust acting on it.
Uniform motion
No acceleration
Vector
Quantity with both magnitude and velocity
Velocity-time graph
Graph showing the velocities on a journey. Velocity on y axis Time on x axis Gradient is acceleration Area under graph is displacement
Work done
In a mechanical system is the product of a force and the distance moved in the direction of the force
v=s/t
v=velocity (m/s)
s=displacement (m)
t=time (s)
s=ut+1/2at^2 v=u+at v^2=u^2+2as s=vt-1/2at^2 s=((u+v)/2)t
s=displacement (m) u=initial velocity (m/s) v=final velocity (m/s) a=acceleration (m/s^2) t=time (s)
Which of the following are both vector quantities? A - acceleration and speed B - displacement and velocity C - mass and time D - power and weight
B
displacement and velocity
As the speed of a cyclist increases, the air resistance acting on him becomes
proportional to the square of his speed.
i.e. air resistance = constant × speed2
The cyclist has a power output P when travelling at a certain constant speed. He then
doubles his speed.
Calculate his new power output as a multiple of P.
Power = (force × distance) /time
P = ((kv^2)× d)/t
New power = (k((2v)^2)× 2d)/t
New power = 8((kv^2)× d)/t = 8P
A car of mass m travelling with a velocity v comes to rest over a distance d in time t.
The constant frictional force acting on the car while it is braking is found using:
A - mv/2t
B - 2mv/t
C - (m(v^2))/2d
D - (2m(v^2))/d
C
A passenger is standing in a train. The train accelerates and he falls backwards.
Use Newton’s first law of motion to explain why he falls backwards.
ΣF =/> 0
An unbalanced/net/resultant/total/ΣF force of zero gives constant speed/velocity/motion
The friction between floor and feet accelerate the feet
or
Thefriction between floor and feet creates an unbalanced/net/resultant/total force on feet
The train accelerates but the man continues travelling at the original/constant speed // the top half has no (resultant) force as the train accelerates
or
The man’s speed relative to the train is lower
or
(All of the) man needs to accelerate at the same rate as the train
a = v^2/r a = r(w^2)
a = centripetal acceleration (ms^-1) v = velocity (ms^-1) r = radius (m) w = angular velocity (rad s^-1)
