Answer 1

A motion represents simple harmonic motion if it is governed by the force law:

F = –kx

ma = –k

`:. a = k/m  x`

Where,

F is the force

m is the mass (a constant for a body)

x is the displacement

a is the acceleration

k is a constant

Among the given equations, only equation a = –10 x is written in the above form with `k/m = 10`

Hence, this relation represents SHM.

Answer 2

Only (c) i.e., a = – 10x represents SHM. This is because acceleration is proportional and opposite to displacement (x).