Question

2
In 1987, the fastest auto race in the United States was the Busch Clash in Daytona, Florida. That year, the
winner's average speed was about 318 km/h. Suppose the kinetic energy of the winning car was 3.80 MJ. What
was the mass of the car and its driver?

Answer 1

Since the winner's average speed was about 318 km/h and the kinetic energy of the winning car was 3.80 MJ. So, the mass of the car and its driver is 974 kg.

Kinetic energy

The kinetic energy of the car is given by K = 1/2mv² where

• m = mass of car and driver and
• v = average speed of car = 318 km/h = 318 × 1000 m/3600 s = 88.33 m/s

Mass of the car and driver

Making m subject of the formula, we have

m = 2K/v²

Since K = 3.80 MJ = 3.80 × 10⁶ J, substituting the values of the variables into the equation, we have

m = 2K/v²

m = 2 × 3.80 × 10⁶ J/(88.33 m/s)²

m = 7.6 × 10⁶ J ÷ (7802.78 m²/s²)

m = 7600000 J ÷ 7802.78 m²/s²

m = 974.01 kg

m ≅ 974 kg

So, the mass of the car and its driver is 974 kg

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