While sewing, a person often wets the end of a thread before, trying to put it through the eys of the needle. Why?

Explain why (a). To keep a piece of paper horizontal, you should blow over, not under, it (b). When w try to close a water tap with our fingers, fast jets of water gush through the openings between our fingers (c). The size of the needle of a syringe controls flow rate better than the thumb pressure exerted by a doctor while administering an injection (d). A fluid flowing out of a small hole in a vessel results in a backward thrust on the vessel (e). A spinning cricket ball in air does not follow a parabolic trajectory.

In the figure shown, the mass of the hanging block is m, while that of the black resting on the floor is 3m. The floor is horizontal and frictionless and all pulleys ideal. The system is initially held stationary with the inclined thread making an angle theta = 30^(@) with the horizontal. The blocks are now released from rest and allowed to move. the hanging block falls through a height (49.5) m before hitting the floor. it is found that the value of theta becomes 60^(@) , when the hanging block hits the floor. Find the speed with which the hanging block hits the floor.

A resistance heater was wound around a 5.0g metallic cylinder. A current of 0.84 A was passed through the heater for 20s while the drop in voltage across the heater was 50V . The temperature change of the cylinder was from 25^(@)C before the heating period and 35^(@)C at the end. If the heat loss is neglected, what is the specific heat of the cylinder metal in cal g^(-1)K^(-1) .