Therefore, the total nucleon number (mass number) doesn’t change, but the
number of protons (the atomic number) increases by one.
- A Since the mass number decreased by 4 and the atomic number decreased by
2, this is an alpha decay.
- B After 3 half-lives, the activity will drop to its initial value,
and after 4 half-lives, it will drop to its initial value. Since is
between and , the time interval in this case is between 3 and 4 half-lives,
that is, between 3(2.5 h) = 7.5 h and 4(2.5 h) = 10 h. Only (B) is in this range.
- B In order to balance the mass number (the superscripts), we must have 2 + 63
= 64 + A, so A = 1. In order to balance the charge (the subscripts), we need 1
- 29 = 30 + Z, so Z = 0. A particle with a mass number of 1 and no charge is
a neutron,.
- E To balance the mass number (the superscripts), we must have 196 + 1 = 197
- A, so A = 0. To balance the charge (the subscripts), we need 78 + 0 = 78 +
Z, so Z = 0. The only particle listed that has zero mass number and zero
charge is a gamma-ray photon,.
- C Radar waves are electromagnetic waves, and the speed of all
electromagnetic waves through empty space is measured by all observers to
always be c (Postulate 2 of the theory of special relativity).
- B Special relativity dictates that length contracts for objects moving at
relativistic speeds, so the length should be smaller. That’s (C). (Bear in mind
that the speed is attainable because the square root of 3 is less than 2, so the
speed is less than the speed of light.) Mathematically, you could calculate the
length as follows. If v = ( )c, then the relativistic factor is
