Romy bowls a 6 kg bowling ball down a lane at 4 m/s.
The ball carries energy because it moves. How much, exactly?
The energy an object has because it is moving is called its kinetic energy.
Count the ball's joules in three short steps.
Half the mass: 0.5 × 6 = 3.
The speed squared: 4 × 4 = 16.
Multiply the two: 3 × 16 = 48. The ball's kinetic energy is 48 J.
With the mass in kilograms and the speed in meters per second, KE comes out in joules, the same joules work is measured in.
A 3 kg terrier sprints across a yard at 4 m/s. Enter its kinetic energy in J.
Earlier in the course you met scalars: quantities with size but no direction. Kinetic energy is a scalar.
A ball has the same KE moving east or west at 5 m/s: the direction never enters the count.
Talia says: 'A 2 kg goose flying east at 8 m/s has exactly the same kinetic energy as it would flying west at 8 m/s.' Is Talia correct?
A 0.5 kg basketball rolls across a court at 6 m/s. Calculate its kinetic energy.
Write down the values:
m = 0.5 kg, v = 6 m/s, KE = ?
Write down the equation:
KE = ½mv²
Half the mass: 0.5 × 0.5 = 0.25. The speed squared: 6 × 6 = 36.
Substitute in the values, and calculate:
KE = 0.25 × 36 = 9
The basketball's kinetic energy is 9 J.
A 1200 kg car drives at 10 m/s. Calculate its kinetic energy.
Write down the values:
m = 1200 kg, v = 10 m/s, KE = ?
Write down the equation:
KE = ½mv²
Half the mass: 0.5 × 1200 = 600. The speed squared: 10 × 10 = 100.
Substitute in the values, and calculate:
KE = 600 × 100 = 60000
The car's kinetic energy is 60000 J.
A 0.25 kg baseball is thrown at 30 m/s. Enter its kinetic energy in J.
A 4 kg drone flies north at 6 m/s, and later flies south at 6 m/s. Which statement about its kinetic energy is correct?
Soren calculates the kinetic energy of a 10 kg sled moving at 3 m/s. Which calculation is correct?
The energy an object has because it is moving is called its ___.