Apiece of wood with a density of 706 kg/m3 is tied with a string to the bottom of a water-filled flask. the wood is completely immersed. suppose the flask with the wood tied to the bottom is placed on a scale. at some point the string breaks and the wood rises to the surface where it floats.

part a

when the wood is floating, is the reading on the scale greater than, less than, or equal to its previous reading?

part b

choose the best explanation from among the following:

when the block is floating it no longer pulls upward on the flask; therefore, the reading on the scale increases.
the same mass is supported by the scale before and after the string breaks, and therefore the reading on the scale remains the same.

Chapter 23, problem 075 the figure shows a geiger counter, a device used to detect ionizing radiation (radiation that causes ionization of atoms). the counter consists of a thin, positively charged central wire surrounded by a concentric, circular, conducting cylindrical shell with an equal negative charge. thus, a strong radial electric field is set up inside the shell. the shell contains a low-pressure inert gas. a particle of radiation entering the device through the shell wall ionizes a few of the gas atoms. the resulting free electrons (e) are drawn to the positive wire. however, the electric field is so intense that, between collisions with gas atoms, the free electrons gain energy sufficient to ionize these atoms also. more free electrons are thereby created, and the process is repeated until the electrons reach the wire. the resulting "avalanche" of electrons is collected by the wire, generating a signal that is used to record the passage of the original particle of radiation. suppose the radius of the central wire is 24 âµm, the inner radius of the shell 2.3 cm, and the length of the shell 14 cm. if the electric field at the shell's inner wall is 2.8 ă— 104 n/c, what is the total positive charge on the central wire?