Chapter 11 - momentum etc Flashcards
What is the symbol for momentum?
p
What is the equation for momentum?
momentum = mass * velocity P = mv
Is momentum a vector or scalar quantity?
vector
What is a vector quantity?
A quantity with a magnitude and a direction
What is always conserved in a collision?
momentum and energy
What must the total momentum be after a collision?
Equal to the total momentum before (to conserve momentum)
How is a rocket propelled in space?
The rocket ejects exhaust gases which travel away from the rocket with a velocity and so momentum
To conserve momentum, the momentum after ejection must equal zero
To achieve this the rocket moves away in the opposite direction, with an equal but opposite momentum
What is Newton’s first law of motion?
The velocity of an object will not change unless a resultant force acts upon it
What is acceleration?
A change in speed or a change in direction
What causes an acceleration?
A resultant force
What is Newton’s second law?
The rate of change of momentum is directly proportional to the resultant force which acts on the object
What is Newton’s second law as an equation?
Force = change in momentum/time F = Δp/Δt
If the mass is constant, how can Newton’s second law be written?
resultant force = mass * acceleration
F=ma
In what direction will an acceleration always be?
The same direction as the resultant force which caused it
When does F=ma not work?
When an object is accelerating at close to the speed of light, so its mass is changing
What is Newton’s third law?
If an A object exerts a force on object B, then object B will exert an equal and opposite force on object A
What type must the two forces in a pair be for Newton’s third law?
They can be any type but the two forces in the pair have to be of the same type
eg both electrical forces or both gravitational forces
Why is a book resting on a table not an example of Newton’s third law?
- Both forces are acting on the same object
- The forces are not the same type
When is work done?
When energy is transferred
What is work?
The amount of energy transferred from one form to another when a force causes some kind of movement
What is the equation for work?
work = force * distance moved in the direction of force W = Fs
What is the symbol for work?
W
What are the units of work?
J
What is the definition of one joule?
The work done when a force of 1N moves an object through a distance of 1m
How can work done be found graphically?
The area under a force vs distance moved graph
What is the equation for force used if the direction of movement is not in the same direction as the direction of force?
W = Fscosθ
What is the principal of conservation of energy?
Energy cannot be created or destroyed. Energy can be transferred from one form to another but the total amount of energy in a closed system will not change.
What is the formula for efficiency?
efficiency = useful power output/total power input
What is the formula for power?
power = work done/time
What are the two equations for kinetic energy?
E = 1/2mv^2
E =p^2/2m
What is the equation for gravitational potential energy?
E = mgΔh
What is the equation for elastic potential energy?
E = 1/2kx^2
How many radians are there in one complete circle?
2π
How do you convert from degrees to radians?
multiply by 2π/360
How do you convert from radians to degrees?
divide by 2π/360
What is 45 degrees in radians?
π/4
What is 90 degrees in radians?
π/2
What is 180 degrees in radians?
π
What is angular speed?
The angle an object rotates through per second