The ignition system of an automobile produces sparks to ignite the fuel in the engine. during each spark process, charges suddenly accelerate through a spark plug wire and across a spark plug's narrow gap. sometimes this process introduces noise into your radio reception. why?

as charge accelerates through the spark plug wires they are emitting radio waves.

as charge accelerates through the spark plug wires they are emitting a changing electric field as well as a changing magnetic field.

as charge accelerates through the spark plug wires they are emitting an electromagnetic wave.

all of the above choices are correct.

According to social exchange theory, altruistic behaviors benefit the individual who performs them.

The percent efficiency of a machine can never be 100% (or greater), because in the real world some energy is always converted into a. heat b. work c. input force d. output force

Part f - example: finding two forces (part i) two dimensional dynamics often involves solving for two unknown quantities in two separate equations describing the total force. the block in (figure 1) has a mass m=10kg and is being pulled by a force f on a table with coefficient of static friction îľs=0.3. four forces act on it: the applied force f (directed î¸=30â above the horizontal). the force of gravity fg=mg (directly down, where g=9.8m/s2). the normal force n (directly up). the force of static friction fs (directly left, opposing any potential motion). if we want to find the size of the force necessary to just barely overcome static friction (in which case fs=îľsn), we use the condition that the sum of the forces in both directions must be 0. using some basic trigonometry, we can write this condition out for the forces in both the horizontal and vertical directions, respectively, as: fcosî¸â’îľsn=0 fsinî¸+nâ’mg=0 in order to find the magnitude of force f, we have to solve a system of two equations with both f and the normal force n unknown. use the methods we have learned to find an expression for f in terms of m, g, î¸, and îľs (no n).