Final answer:
The kinetic energy of a 70 kg system (a 20 kg bicycle with a 50 kg girl) traveling at 8 m/s is calculated to be 2240 joules using the formula KE = ½mv².
Step-by-step explanation:
The kinetic energy (KE) of an object is given by the equation KE = ½mv², where m is the mass of the object and v is its velocity. In the case of a 20 kg bicycle carrying a 50 kg girl traveling at a speed of 8 m/s, the total mass (m) is the sum of the mass of the girl and the bicycle, which is 70 kg. Therefore, the kinetic energy can be calculated as follows:
KE = ½ × 70 kg × (8 m/s)²
KE = ½ × 70 kg × 64 m²/s²
KE = 35 kg × 64 m²/s²
KE = 2240 J (joules)
Thus, the kinetic energy of the girl and the bicycle together, traveling at 8 m/s, is 2240 joules.