Question

A body covers distance of x metre along a semicircular path . calculate the magnitude of displacement of the body and the ratio of distance to displacement

Answer 1

Ok then, now we know that:
d=  x metres
Path= semicircular

I.e. 1/2x(2$\pi$r)=x                                                 (r=radius)
    =$\pi$r=x                                                             . . .(1)

Now, since a semi-circle is covered, displacement= diameter (since a chord formed by semicircle is the diameter)
Therefore, displacement=y= diameter= 2r                           . . .(2) (ans a)

Now, from statements (1) and (2)
Distance : Displacement = x : y
⇒ $\pi$r : 2r
⇒ $\pi$ : 2                                                                 . . .(ans b)

Hope this helped, also if you want you can further reduce the final answer by assuming pi as 22/7 if necessary. 

Answer 2

so,here is your answer:

Circumference of semicircle is given by-$\pi r$
Body cover distance-x
Hence,x=$\pi r$,is the distance actually covered by the body
Displacement means shortest distance between initial and final point that is diameter =2r
So,Displacement : Distance
       =2r:$\pi r$
       =2:$\pi$
       =7:11