Two loudspeakers, L1and L2, have the same frequency and
are in phase with each other.
An interference pattern is
produced

At position P, which is the same distance from both loudspeakers, there is a maximum. The next
maximum is at position R, where L R = 2.8 m and L R = 2.5 m.
The speed of sound in air is 340 m st. The frequency of the sound emitted by the loudspeakers is:
(A) 2.0 x 102 Hz
(B) 2.3 x 102 Hz
(C) 5.7x 102 Hz
(D) 1.1 x 103 Hz

Assuming weightless pulleys and 100% efficiency, what is the minimum input force required to lift a 120 n weight using a single fixed pulley?

Comedians like to joke that the reason we haven’t been visited by intelligent life from elsewhere in the universe is that aliens have been monitoring earth’s broadcasts of intellectually embarrassing tv programs, like gilligan’s island, fear factor, the jersey shore, and the jerry springer showand so consider us far too primitive to merit a visit. let’s check the assertion that aliens could have been receiving them. tv programs are broadcast at a frequency of about 100mhz with about 100kw of total power in 30frames per second, which emanatesroughly uniformly in all directions. assume that interstellar space transmits these broadcasts without attenuation. no matter how smart they are, aliens would require at least one photon per frame to interpret our signals. findthe number of photons per unit time per unit area reaching a receiver on a possible planet in the nearest star system, which is about 4 light-years away (a light-year is the distance light travels in a year). if aliens aimed a receiver or detector directly at earth, how big (in diameter) would it have to be to receive a photon per frame

What is the energy of a photon of ultraviolet radiation with a frequency of 4.4 × 1015 hz? planck’s constant is 6.63 × 10–34