If a rock has 30 parent atoms and 90 daughter atoms, how many half-lives has it gone through?

Search coils and credit cards. one practical way to measure magnetic field strength uses a small, closely wound coil called a search coil. the coil is initially held with its plane perpendicular to a magnetic field. the coil is then either quickly rotated a quarter-turn about a diameter or quickly pulled out of the field. (a) derive the equation relating the total charge q that flows through a search coil to the magnetic-field magnitude b. the search coil has n turns, each with area a, and the flux through the coil is decreased from its initial maximum value to zero in a time ∆t. the resistance of the coil is r, and the total charge is q = i∆t, where i is the average current induced by the change in flux. (b) in a credit card reader, the magnetic strip on the back of a credit card is rapidly “swiped” past a coil within the reader. explain, using the same ideas that underlie the operation of a search coil, how the reader can decode the information stored in the pattern of magnetization on the strip. (c) is it necessary that the credit card be “swiped” through the reader at exactly the right speed? why or why not?

Can you match these to the correct definition

Pressure is a measure of force per unit area or p=f/ap=f/a. a student is checking the amount of pressure their car exerts upon the road. the car weighs 22 tons ( us short ton ). the student finds the dimensions of each tire's footprint on the road is 12.5 cm x 16.5 cm. in pounds per square inch (psi), what is the total pressure the car exerts upon the road?