Year 10 - All 3 Science Sections revision
Physics
Chemistry
Biology
Kinetic Energy
Amount of Kinetic energy of an object depends on its: Mass, Speed
Calculating kinetic energy
KE = ½ mv2 or KE = ½ × m × v2
KE = the kinetic energy in joules, J
m = the mass in kilograms, kg
v = the speed in metres per second, m/s
EXAMPLE: what is the kinetic energy of a 1000 kg car travelling at 5 m/s?
KE = ½ × 1000 × 52 = 500 × 25 = 12500 J
Gravitational potential energy (GPE)
Amount of gravitational potential energy an object on earth has depends on its: mass, height above the ground
GPE (J) = mass (kg) x gravitational field strength (or 'g') (N/kg) x height (m) GPE = m x g x h
Place Gravitational field strength
Earth 10N/kg
Moon 1.6N/kg
Jupiter 26N/kg
Example:
Question
On Earth, a ball of mass 0.5kg is kicked straight up. How much GPE does it have at its highest point 6m off the ground?
Answer
GPE = 0.5 x 10 x 6 = 30J
Question
On the Moon, if the same ball were given the same amount of GPE, how high would it have to be above the surface?
Answer
h = GPE / (m x g) = 30 / (0.5 x 1.6) = 37.5m
Weight (N) = mass (kg) x gravitational field strength (N/kg) w = m x g
Question
On Earth, what is the weight of a person whose mass is 45kg?
Answer
w = m x g = 45 x 10 = 450N
Power
Question
An electric lamp transforms 500 J in 5 s. What is its power?
Answer
Question
Which is the best fuse to use (3A, 5A or 13A) with a 1.15 kW electric fire at a potential difference of 230 V?
Remember that 1.15 kW is 1,150 W
Answer
Energy transfer
Sankey diagram
