Physics

Problem

A runner covers

60\,\text{m}

30\,\text{s}

and then

40\,\text{m}

10\,\text{s}

along a straight track. She wishes to adjust only the time taken for the second

40\,\text{m}

so that her entire

100\,\text{m}

run is at a uniform speed equal to her speed during the first

60\,\text{m}

. Which of the following new times for the second part will achieve this? a)

30\,\text{s}

18\,\text{s}

20\,\text{s}

25\,\text{s}