Question

A particle is moving in a circular path of radius 'r'. What will be the distance and displacement after half revolution?

Answer 1

Distance is the actual path moved by the particle. In this case, it would be the circumference of a semi circle. Its formula will be
$\frac{2\pi \: r}{2} \\ = \pi \: r$
Displacement would be the distance between the starting point and the ending point of the motion of the particle. Here, it would be the diameter of the circle, which will be 2r.