3.3 Work, energy, and power

Question 1

how is work done defined

Answer 1

product of the force and the displacement change in the direction of the force

Question 1

whats the equation for work done

Answer 1

W=Fs

Question 2

what are the units of work done

Answer 2

Joules ( J )

Question 3

why is work done when you lift an object off the ground

Answer 3

The force you are exerting is equal in magnitude and opposite in direction to the force of gravity

Question 4

what is the energy transfer when an object is lifted off the ground

Answer 4

the object has gained Gpe

Question 5

how is energy defined

Answer 5

the capacity to do work

Question 6

how do you calculate work done when the force is applied at an angle to the direction in which the object moves

Answer 6

W=Fxcosθ

Question 7

is energy a scalar of vector quantity

Answer 7

scalar

Question 8

what is the SI unit of energy

Answer 8

Joule ( J )

Question 9

how is efficiency calculated

Answer 9

efficiency=(useful output energy/ total input energy) x100

Question 10

what does it mean if something has a high efficiency

Answer 10

little energy is wasted

Question 11

what are the two general classifications of energy for systems with mass-describe them

Answer 11

kinetic energy: energy due to the movement of an object
gravitational potential energy: energy due to the position of an object in the earths gravitational field

Question 12

state the principle of conservation of energy

Answer 12

the total energy of a closed system remains constant: energy can never be created or destroyed but it can be transferred from one form to another

Question 13

what does the term potential energy mean

Answer 13

often used to mean ‘hidden’ or stored

Question 14

give two examples of potential energy

Answer 14

elastic potential energy: energy stored in an object as a result of reversible change in its shape
electrical potential energy: energy of electrical charges due to their position in an electric field

Question 15

how is kinetic energy calculated

Answer 15

Ek=1/2mv2

Question 16

how is kinetic energy related to mass for objects travelling at the same speed

Answer 16

kinetic energy is directly proportional to the mass

Question 17

what is gravitational potential energy

Answer 17

the stored energy of an object has by virtue of being in a gravitational field

Question 18

how is gravitational potential energy calculated

Answer 18

Gpe= mgΔh

Question 19

give an example in which GPE and KE are exchanged

Answer 19

mgh=1/2mv2 as an object falls Gpe decreases and Ek increases

Question 20

give an expression for the final speed (v) of an object of mass (m) dropped from a height (h) located on earth- state any assumptions

Answer 20

v=√2gh theres no resistive forces, the mass of the object has no bearing on its final speed

Question 21

define power

Answer 21

the rate of transfer of energy/ work done (with respect to time)

Question 22

state the equation of power

Answer 22

power= energy transferred/ time P=W/t

Question 23

give two alternative units of power

Answer 23

J/s or Watts (W)