Question

A person is running along a circular track of area $625\pi m^2(\pi =\frac{22}{7})$ with a constant speed. Find the displacement in $15$ seconds if he has to complete the race in $30$s.

Answer 1

area of circular track$=625m^2$

$r^2=625$

$r^2=625$ will get cancelled when it will go on L.H.S.

$r=\sqrt{625}$

$r=25$

perimeter of circular track $=2\pi r=2\times \frac{22}{7}\times 25=44\times \frac{25}{7}=\frac{1100}{7}=157.14m$

the person has to run a distance of $157.14m$

speed of person$=\frac{distance}{time}$

distance$=157.14m$

time$=30seconds$

$speed=\frac{157.14}{30}=5.23m/s$

displacement$=speed\ast time$

time$=15seconds$

speed$=5.23m/s$

displacement$=5.23\ast 15$

displacement in 15 seconds $=78.45m$