In longitudinal waves, the particles of the medium or a system displaces back and forth(parallel) in the direction of the propagation of waves. In transverse waves, the particles of the medium or a system displaces perpendicular to the direction of the propagation of waves. Therefore, C is correct.
Explanation:
so as to reduce the force of friction on the hinges and also to make the hinges to move freely
A single reflection, like shouting at the side of a mountain and hearing
your voice come back to you, is an 'echo'.
Multiple reflection, like clapping your hands once inside a large room,
is 'reverberation'.
Expand each vector into their component forms:
Similarly,
Then assuming the resultant vector is the sum of these three vectors, we have
and so has magnitude
and direction such that