To determine which object has the greatest kinetic energy, we use the kinetic energy formula:
\[ KE = \frac{1}{2}mv^2 \]
where \( KE \) is kinetic energy, \( m \) is mass, and \( v \) is velocity.
Given the mass of all cars is 500 kg, we can calculate the kinetic energy for each:
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Green Car (500 kg, 21 m/s): \[ KE = \frac{1}{2} \times 500 \times (21)^2 = \frac{1}{2} \times 500 \times 441 = 110250 \text{ J} \]
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Yellow Car (500 kg, 12 m/s): \[ KE = \frac{1}{2} \times 500 \times (12)^2 = \frac{1}{2} \times 500 \times 144 = 36000 \text{ J} \]
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Blue Car (500 kg, 30 m/s): \[ KE = \frac{1}{2} \times 500 \times (30)^2 = \frac{1}{2} \times 500 \times 900 = 225000 \text{ J} \]
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Red Car (500 kg, 3 m/s): \[ KE = \frac{1}{2} \times 500 \times (3)^2 = \frac{1}{2} \times 500 \times 9 = 2250 \text{ J} \]
Now, comparing the kinetic energies:
- Green Car: 110250 J
- Yellow Car: 36000 J
- Blue Car: 225000 J
- Red Car: 2250 J
The blue car has the greatest kinetic energy at 225,000 J.