We are given:
Initial Velocity(u) = 15 m/s
Time interval(t) = 20s
Solving for the distance covered:
Since the girl keeps riding her bike at 15 m/s, her speed is constant and hence, acceleration of the bike is 0 m/s²
acceleration(a) = 0 m/s²
We know that:
s = ut + 1/2(at²) [second equation of motion]
s = (15)(20) + 1/2(0)(400) [plugging the values]
s = 150 + 0
s = 300 m
Hence, the girl covered 300 m in 20 seconds