1.

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

Answer»

The correct answer is

All.

(a) F x a.

(b) v x r .

(c) 
a x r.

(d) F x r.

EXPLANATION: 

The cross product is a vector itself and its magnitude is the product of the magnitudes of the vectors and the sine of the angle between them. If the vectors are parallel or anti-parallel i.e. if the angle between them is zero or π, its sine becomes zero and the cross product becomes zero. 

Here all the vectors are along the same line either in the same direction or in opposite direction. Hence all options are zero. 



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