Question

A block of mass $(m=1kg)$ is released from rest over a circular curved path, as shown in diagram. The work done (in joules) by normal force, when block is displaced by $\theta ={45}^{\circ }$ is

Answer 1

Normal force is always perpendicular to surface of contact and displacement is along surface of contact.
So, the angle between normal force and displacement is ${90}^{\circ }$
Work done by normal force is $W=Ndcos\theta$
$W=Ndcos{90}^{\circ }=0$