An ideal gas expands adiabatically ($\gamma = 1.5$). To reduce the r.m.s. velocity of the molecules 3 times the gas has to be expanded

A simple pendulum oscillates with an angular amplitude $\theta$. If the maximum tension in the string is twice the minimum tension then $\theta$ is

A spring executes S.H.M. with mass 10 kg attached to it. The force constant of spring is 10 N/m. If at any instant its velocity is 40 cm/s, the displacement at that instant is
(Amplitude of S.H.M. is 0.5 m)

Waves having a velocity 10m/s, strike a stationary boat near the sea shore. The distance between two consecutive crests of the waves is 40m. After how many second, the consecutive waves strike the boat?