CH5 Flashcards
Define Work Done
Product of the force and distance moved in the direction of the force
What is the formula for work?
W = F * x
where: F is the force and x is the direction moved in the distance of the force
What is meant by work?
Work is the amount of energy transferred when an external force causes an object to move over a certain distance
What is the unit of Work?
Jules or Nm. 1J=1Nm
How is work done calculated when the force is applied at an angle to the direction at which the object moves?
W = (F cos theta) * x
where theta is the angle between F and the direction of motion
What is meant by energy?
Energy is the capacity of doing work
Is energy scalar or vector?
Scalar qty
What is the SI unit for energy
Joule
What is kinetic energy? Examples?
energy due to movement of objects with mass.
Examples: moving car, moving atoms
What is Gravitational potential energy? Examples?
energy due to the position of an object in the Earth’s gravitational field
Examples: child at top of a slide, water held in clouds
What is meant by “potential” in physics?
It is often used to mean “hidden” or “stored”
What is chemical energy? Examples?
Energy contained within the chemical bonds between atoms. It can be released when the atoms are rearranged.
Examples: energy stored in a chemical cell, energy stored in petrol and released when it burns
What is elastic potential energy? Examples?
energy stored in an object as a result of reversible change in shape.
Examples: a squashed spring, a stretched guitar spring
what is electrical potential energy? Examples?
Energy of electrical charges due to their position in an electric field.
Examples: static energy on a charged balloon, electrical charges on a thundercloud
What is nuclear energy? Examples?
Energy within the nuclei of atoms - it can be released when the particles with the nucleus are rearranged.
Examples: energy from fusion processes in the Sun, energy from nuclear fission reactors
What is radiant (or electromagnetic energy)? Examples
energy associated with all electromagnetic waves, stored within the oscillating electric and magnetic field.
Examples: energy from the hot sun, energy from an LED
What is meant by sound energy? Examples?
Energy of mechanical waves due to the movement of atoms. Examples: energy emitted when you clap, output of energy from your headphones
What is meant by internal (heat or thermal) energy? Examples?
The sum of the random potential and kinetic energies of atoms in a system.
Examples: a hot cup of tea has more thermal energy than a cold one
What does the principle of conservation of energy state?
The total energy in a closed system remains constant. Energy cannot be created or destroyed, it can only be transferred
What is the formula of Kinetic Energy for an object in linear motion?
Ek = 1/2 m(v)2
Where m is mass and v is speed
What is Ek directly proportional to?
Sq root of its speed
How is Ek for objects travelling at same speed?
Directly proportional to their mass
What is the formula of Gravitational Potential Energy?
Ep = mgh
where ms is mass, h is change in height, g is acceleration of free fall (9.81ms2 for objects close to earth)
When is Ep lost?
When height decreases
When is Ep gained?
When height increases
What is the equation to calculated final speed form Ek and Ep? when is it valid?
v = square root of 2gh.
Only valid if there are no resistive forces
Derived from mgh = 1/2m(v)2
What is power?
Power is the rate of work done
Formula for power
P = W/t
What is the unit pf measure of Power?
Js-1 or Watts (W). 1W=1Js-1
How do you find speed when a constant force is needed to maintain a constant speed?
v = F/P
What does the work-energy theorem state?
The work-energy theorem states that the work done on an object is equal to the change in its kinetic energy.
Define efficiency
(Useful output energy/ Useful input energy) * 100%
If you are given initial kinetic energy and work done how do you calculate Final Kinetic energy?
Initial kinetic energy - Work done = Final kinetic energy
What is the definition of watt
Joule per second
What is the relationship between P, the rate of work done against a frictional force, and the speed v of an object?
P directly proportional to (v)3
What is the formula to calculate the work done by a couple?
work done = 2 × work done by each force
Describe how the kinetic energy of the arrow changes during its journey from when it is fired until it reaches its
maximum height.
(Kinetic energy) reduces (with height)
At maximum height, KE is minimum
What is the formula to calculated the total energy provided to do n activity when you are given the power output and the time the output is applied for (3.3. Q57)
E = P*t
How do you calculate forward force if given power and velocity?
F = P/v
