A particle executes simple harmonic motion (SHM) about its mean position. The restoring force on it is:
ADirectly proportional to displacement and in the same direction
BDirectly proportional to displacement and opposite to displacement
CInversely proportional to displacement
DIndependent of displacement
Answer & Solution
Correct answer: B. Directly proportional to displacement and opposite to displacement
SHM is defined by a linear restoring force: $F = -kx$. The minus sign is essential. Magnitude grows with displacement (proportional to $x$), direction always points back toward the mean position.
The equation of motion $m\ddot x = -kx$ has the angular frequency $\omega = \sqrt{k/m}$, period $T = 2\pi/\omega = 2\pi \sqrt{m/k}$.
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