Question

Which of the following quantities are always zero in a simple harmonic motion?
(a) →F× →a.
(b) →v× →r.
(c) →a× →r.
(d) →F× →r.

Answer 1

Answer:

direction of force and acceleration always same in SHM so both are zero....

Answer 2

$\rightarrow F_{\cdot} \rightarrow a$ quantities are always zero in a simple harmonic motion.

Explanation:

• It is to be noted that $\rightarrow v \times \rightarrow r, \rightarrow a \times \rightarrow r$ and $\rightarrow F \times \rightarrow r$ are either anti-parallel or parallel to each other.
• And, zero will be the result of their cross products.  
• It is to be noted that $\rightarrow F . \rightarrow r$ will be negative always. It is also to be understood that the acceleration has to be in the identical direction as the force is shown as $\rightarrow a_{.} \rightarrow r$. So, this will also be seen in negative always.