Do now! How much energy sort ? He’s going to blow! Be careful Good Neutral Excellent MOODOMETER

Today’s lesson Calculating Gravitational Potential energy Calculating kinetic energy

A reminder Energy cannot be made or destroyed, only transformed (changed). Energy is measured in Joules. That’s me!

Types of Energy HeatChemical LightGravitational SoundElastic/strain KineticNuclear Electric Stored/potential

Gravitational potential energy E p = mgh Can you copy this please? We will learn in later lessons where this formula comes from. J kg N/kg or m/s 2 m

Example A dog of mass 12 kg falls from an aeroplane at a height of 3.4 km. How much gravitational energy does the dog have as it leaves the aeroplane? Woof! (help!)

Example On earth g = 10 m/s 2 Height = 3.4 km = 3400 m Mass of dog = 12 kg

Example On earth g = 10 m/s 2 Height = 3.4 km = 3400 m Mass of dog = 12 kg GPE of dog = mgh = 12 x 10 x 3400 = J

Example GPE of dog = mgh = 12 x 10 x 3400 = J Just before the dog hits the ground, what has this GPE turned into?

Kinetic energy

Kinetic energy of an object can be found using the following formula E k = mv 2 2 where m = mass (in kg) and v = speed (in m/s)

Example A bullet of mass 150 g is travelling at 400 m/s. How much kinetic energy does it have?

Example A bullet of mass 150 g is travelling at 400 m/s. How much kinetic energy does it have? E k = mv 2 /2 = (0.15 x (400) 2 )/2 = J

Energy changes

Example GPE of dog = mgh = 12 x 10 x 3400 = J Just before the dog hits the ground, what has this GPE turned into? Kinetic energy

Example GPE of dog = mgh = 12 x 10 x 3400 = J KE at bottom = J Just before the dog hits the ground, what has this GPE turned into? Kinetic energy

Example GPE of dog = mgh = 12 x 10 x 3400 = J KE at bottom = J = mv 2 /2 Just before the dog hits the ground, what has this GPE turned into? Kinetic energy

Example = mv 2 /2 Just before the dog hits the ground, what has this GPE turned into? Kinetic energy

Example = mv 2 /2 2 x = 12 x v 2 Just before the dog hits the ground, what has this GPE turned into? Kinetic energy

Example = mv 2 /2 2 x = 12 x v = 12v 2 Just before the dog hits the ground, what has this GPE turned into? Kinetic energy

Example = mv 2 /2 2 x = 12 x v = 12v = v 2 Just before the dog hits the ground, what has this GPE turned into? Kinetic energy

Example = mv 2 /2 2 x = 12 x v = 12v = v = v v = 261 m/s Assuming no energy is lost as air resistance – in reality the dog would have reached TERMINAL VELOCITY

Let’s try some questions! Stick them in first!

Homework Due next Thursday 14 th April Finish ALL questions on Kinetic and Gravitational energy