Deck 9: Chapter 9 Flashcards
When will something’s velocity not change?
If no resultant force acts on an object, it’s velocity will not change.
Resultant force(N) =
= mass(kg) x acceleration(m/s^2)
What are assumptions made about the F= ma equation?
1) The resultant force is the vector sum of all the forces2) The acceleration is always in the same direction as the resultant force and is measured in ms^-2
Michael and his brother have a race. Michael always wins, why?
Michael is able to exert a greater force than TomMichael is lighter than Tom.
Two divers take the same time to reach the water surface, why? ( Assume no air resistance )
1) The only force acting on them is their weight, mg.2) Since F=ma this gives ma=mg or a= g, their acceleration doesn’t depend on their mass.
What does the word “work” in Physics mean?
The word “Work” means the amount of energy transferred from one form to another when a force causes a movement of some sort.
What is the work done equation?
Work done(W) = force causing motion (F) x distance moved(s)W= Joules
What are some points to remember about the equation W=f x d
1) Work is the energy that’s been changed from one form to another- it’s not necessarily the total energy. ( like moving a book from a shelf to a higher shelf, the work done here would not give the total potential energy)2) The force will be a fixed value in any calculations, it’s either constant or average force.3) The equation gives you the definition “ One joule is the work done when a force of 1 newton moves an object through a distance of 1 metre” .
What do you do if the work done is not in the direction you want it in?
Use trigonometry with resolving forces to work it out.
What is power defined as?
Power is the rate of doing work - the amount of energy transformed from one form to another per second.
What is the power equation?
Power(P) work done(W) / time(t)P= watts
What is the watt defined as?
The watt is defined as a rate of energy transfer equal to 1 joule per second.
What’s another version of the power equation?
Power= force x distance moved / timePower = Force x velocity
What does the principal of conservation of energy say?
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.
Efficiency =
Useful energy output / energy intput
