Tides result from the gravitational (external) forcing of the Moon and Sun on Earth's oceans, so they are an example of forced oscillation.

Higher momentum (more energetic) particles have shorter (extremely small) de Broglie wavelengths, so option B is correct.

If frequency f = n (oscillations per second), the angular frequency ω = 2πf = 2πn rad/s.

Wave speed depends on tension and linear density but not on the location where the string is plucked, as marked in the OCR.

The OCR indicates option B is marked; within the block context it identifies gravitational forces on Earth as the cause (as presented).

Frequency is independent of amplitude; changing amplitude does not change the wave's frequency.

A seconds pendulum has period 2 s giving L ≈ 0.993 m, which is 993 mm.

Wave speed in a string v = sqrt(T/μ); if tension T is quadrupled, v increases by sqrt(4)=2, so it becomes double.

For a simple pendulum T ∝ √L, so L ∝ T^2 giving a parabolic relation between L and T.

Since T ∝ √L, to double T, L must be increased by factor 4 (square of 2).