To determine which object has the greatest kinetic energy, we can use the kinetic energy formula:
\[ KE = \frac{1}{2}mv^2 \]
where:
- \( KE \) is the kinetic energy,
- \( m \) is the mass of the object,
- \( v \) is the velocity of the object.
Since all the cars have the same mass of 500 kg, we can compare their kinetic energies by calculating \( v^2 \) for each car.
-
Green Car:
- \( v = 21 , \text{m/s} \)
- \( v^2 = 21^2 = 441 \)
-
Blue Car:
- \( v = 30 , \text{m/s} \)
- \( v^2 = 30^2 = 900 \)
-
Yellow Car:
- \( v = 12 , \text{m/s} \)
- \( v^2 = 12^2 = 144 \)
-
Red Car:
- \( v = 3 , \text{m/s} \)
- \( v^2 = 3^2 = 9 \)
Now we can summarize the \( v^2 \) values:
- Green Car: 441
- Blue Car: 900
- Yellow Car: 144
- Red Car: 9
The blue car has the highest \( v^2 \) value (900), which means it has the greatest kinetic energy.
So, the answer is: a blue car with a mass of 500 kg moving at 30 m/s.