Pair production can occur if:
A) the energy of two photons is greater than the combined mass-energy of a particle-anti-particle pair.
B) only virtual particles are produced.
C) photons are at the event horizon of a black hole.
D) one particle is struck by a sufficiently high energy photon that a pair of electrons is formed.
E) the particle and antiparticle have opposite spins.
A
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An automobile engine takes in 4000 J of heat and performs 1100 J of mechanical work in each cycle. (a) Calculate the engine's efficiency. (b) How much heat is "wasted" in each cycle?
What will be an ideal response?
A 250 g block is dropped onto a relaxed vertical spring that has a spring constant of k = 2.5 N/cm (Fig. 7-30 ). The block becomes attached to the spring and compresses the spring 12 cm before momentarily stopping. While the spring is being compressed, what work is done on the block by
(a) the gravitational force on it and
(b) the spring force?
(c) What is the speed of the block just before it hits the spring? (Assume that friction is negligible.)
(d) If the speed at impact is doubled, what is the maximum compression of the spring?
What are the characteristics of an open cluster of stars?
A) mostly found above and below the galactic plane B) old age and millions of members C) a few hundred, mainly main sequence stars D) All stars are much more massive than our Sun. E) All stars are about the same age and luminosity.
The geocentric model was formulated before the heliocentric model.
a. true b. false