Answer:
[tex] \frac{v^{2} }{R}[/tex]
Explanation:
[tex]R[/tex] = radius of the loop
[tex]m[/tex] = mass of the block
[tex]v[/tex] = speed of the block at top of the loop at point A
[tex]a[/tex] = magnitude of acceleration of block at A
At point A, the block moves in a circle and hence experience centripetal force. Due to this centripetal force, the centripetal acceleration of the block can be given as
[tex]a = \frac{v^{2} }{R}[/tex]