An electron and a positron, both essentially at rest, annihilate each other, emitting two identical photons in the process. What is the wavelength of these photons?
The mass of an electron or positron is 9.11 × 10-31 kg. (h = 6.626 × 10-34 J ? s, c = 3.00 × 108 m/s)
A) 1.21 × 10-12 pm
B) 1.73 pm
C) 2.42 pm
D) 3.07 pm
E) 3.46 pm
C
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A block slides on a rough horizontal surface from point A to point B. A force (magnitude P = 2.0 N) acts on the block between A and B, as shown. Points A and B are 1.5 m apart. If the kinetic energies of the block at A and B are 5.0 J and 4.0 J, respectively, how much work is done on the block by the force of friction as the block moves from A to B?
A. ?3.3 J B. +1.3 J C. +3.3 J D. ?1.3 J E. +4.6 J
An airplane flying horizontally with a speed of 500 km/h at a height of 800 m drops a crate of supplies (see the following figure). If the parachute fails to open, how far in front of the release point does the crate hit the ground?
How does the explosion of a nuclear bomb provide evidence for the theory of relativity?
A) The bomb converts rest-mass energy into thermal energy in accord with E = mc2, which is part of the theory of relativity. B) The mass of the bomb when it explodes is much greater than its normal mass. C) The bomb causes things in its vicinity to move at high speeds, allowing scientists to measure effects of time dilation. D) The bomb shortens the lifetimes of all people who happen to be near it when it detonates.
If at least one component of a vector is a positive number, the vector cannot
1.have three dimensions. 2.be zero. 3.have any component that is negative. 4.None of these choices is correct.