P. 3837. A wooden planck of mass m stays at rest on a horizontal surface (see the figure). A pointlike object of mass m moves along the horizontal surface with a speed of , and slides onto the circular part of the planck, than flies off (friction is negligible).
a) Find the velocity of the planck after the pointlike object left it.
b) Find the greatest height to which the pointlike object ascends.
P. 3839. A small test tube is placed into a high cylinder which is nearly totally filled with water. The test tube is placed upside down into the water, and in its top a certain amount of air remains, such that the test tube floats. The cylinder is closed by a piece of thin rubber. If the rubber is pressed, the test tube descends and if the excess pressure on the rubber is ceased the test tube ascends. But it comes up only if it did not go below the depth of 2 m. Find the height of the that part of the test tube which was above the water before the cylinder was closed by the piece of rubber. (The mass of the cylinder-shaped test tube is 0.5 g, its inner cross section is 0.5 cm2, and its length is 5 cm. The density of water is 1000 kg/m3, the density of glass is 2500 kg/m3, and the external pressure is 105 Pa.)
P. 3841. In the circuit shown in the figure switch K is turned off for a long time, then it is turned on for a long time. How does the charge of the condenser change?
Data: C=10 F, , Rb1=0.2 , , Rb2=0.4 .