Which of these systems is NOT an “isolated system” to which conservation of momentum can be applied? 1. A billiard ball collides with another billiard ball on a level pool table. (Ignore friction with the table during the instant of the collision.) System: the two balls
2. A ball falls freely toward the ground. (Ignore air friction.) System: the ball and the earth
3. All of these in fact are isolated systems.
4. A single car slips on an icy road. (Friction with the ice is negligible.) System: the car
5. Two cars slipping on an icy road collide with one another. (Friction with the ice is negligible.) System: the two cars
6. A ball falls freely toward the floor. (Ignore air friction.) System: the ball
7. Two masses connected by a spring oscillate on a frictionless tabletop. System: the two masses and the spring

Density of salty water as compared to the density of pure water is(a) is less(b) is always equal(c) is always more(d) may be less or more

The a metal retainer that keeps the rolling elements evenly spaced. n a. seal n b. separator n c. bearing n d outer race

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?