The diagram above represents balls in an undulating surface. Which of the following option represents positions of stable equilibrium?

A bob of weight 0.1 N hangs from a massless string of length 50 cm. A variable horizontal force which increase from zero is applied to pull the bob until the string makes an angle of 60o with the vertical. The work done is?

Two metals P and Q of length l1 and l2 are heated through the same temperature difference. If the ratio of the linear expansivities of P to Q is 2:3 and the ratio of lengths is 3:4. What is the ratio of increase in length of P to Q?

THe velocity of sound in air at 16oC is 340ms-1. What will it be when the pressure is doubled and its temperature raised to 127ºC?

Three capacitors of capacitance 2μF, 4μFand 8μF are connected in parallel and a P.D of 6V is maintained across each capacitor, the total energy stored is?