A student writes the following steps while deriving the equation of motion of a simple pendulum.
(i) Restoring force: Ft=−mgsinθ
(ii) For small θ, replace sinθ by θ
(iii) Therefore Ft=−mgθ
(iv) Using s=Lθ, writes Ft=−mgL
Which step FIRST introduces an error in the derivation?
a) Step (iii)
b) Step (i)
c) Step (iv)
d) Step (ii)