Final answer:
The kinetic energy of a 50-kg girl running at 4 m/s is 400 J, which is calculated using the kinetic energy formula KE = 0.5 x mass x velocity squared.
Step-by-step explanation:
The student has asked about the kinetic energy of a 50-kg girl running along a track at 4 m/s. Kinetic energy is given by the equation KE = 0.5 × m × v2, where 'm' is mass in kilograms and 'v' is velocity in meters per second. Plugging in the given values, KE = 0.5 × 50 kg × (4 m/s)2 = 400 J. Therefore, the girl's kinetic energy is 400 J, which corresponds to option 2).