Mechanics Flashcards
The equation to find the weight of an object
W = mg
Definition of g
g is acceleration due to gravity. Force per unit mass
List the SI base units
Candela - Luminosity KG - mass Moles - amount of substance Amp - current Kelvin - temperature Second - time Metre - length
What’s the difference between a scalar and a vector
A scalar only has magnitude, a vector has magnitude and direction
What’s the gradient of a displacement-time graph
Velocity
What’s the gradient of a velocity-time graph
Acceleration
What’s the area under a velocity-time graph
Displacement
Terminal velocity model answer
As skydiver speeds up, air resistance will increase
Net force on skydiver will decrease, reducing acceleration
Parachute greatly increases the size of the air resistance
When air resistance = weight of skydiver, skydiver is in equilibrium
What do free body diagrams show?
All the forces acting on an object
Derive the base units for force
F = ma [m] = kg [a] =ms^-1 => [F] = kgms^-1
How do you resolve a vector?
Split it into its x and y components using sine and cosine
State Newton’s second law and the two equations for it?
The rate of change of momentum of a body is directly proportional to the external resulting force acting upon it. The change of momentum takes place in the direction of that force. F = ma = p/t
How do you add two vectors?
Split into components then add components then use Pythagoras to combine components
State Newton’s 3rd Law
If object A exerts a force on object B then object B exerts an equal but opposite force back on A
What are the criteria for Newton’s Third Law pairs?
Same type of force, same magnitude, opposite direction
List the SUVAT equations
v = u + at s = ut + 1/2at^2 v^2 = u^2 + 2as s = 1/2(v+u)t s = vt - 1/2at^2
How do you add vectors by scale drawing?
Draw vectors originating from the same point, draw in parallel sides then join corners
How do you solve a projectiles question?
Resolve velocity vector, find time to taken to reach apogee using a = -g, double time to find total time,
Give the equation for momentum
p = mv
State the law of conservation of momentum
Momentum before a collision in a direction is equal to the momentum after a collision
Give the equation for Kinetic Energy
E = 1/2mv^2
Give the equation for Gravitation Potential Energy
E = mgh
State the law of conservation of energy
Energy can neither be created or destroyed therefore it is possible to use mgh = 1/2mv^2
Define Centre of Gravity
from the point from the which the weight would act if the object was considered as a particle
State the principle of moments
If the total clockwise moment is equal to the total anticlockwise moment and the resultant force is 0 then the object is in equilibrium
Equation for moments
M = Fd where d is the perpendicular distance
Equation for efficiency
Energy out/Energy in or Power in/Power out
Give the formula for work done
W = Fdcos x
