The event horizon of a black hole is:
a) the distance at which a star is torn apart by tidal forces
b) the minimum distance from which light can escape
c) the distance at which a human body is torn apart by tidal forces
d) the distance from which we can see inside the black hole
e) the point of infinite density.
Ans: b) the minimum distance from which light can escape
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A brake pad is used to give a normal force of 150N to the outer surface of a 0.25kg spinning disk, in order to slow it down from 250rpm to rest. The disk’s radius is 0.25m. If the coefficient of friction between the pad and the disk is 0.45, how much time was required for the disk to slow from 250 rpm to rest?
A. 0.19s B. 0.55s C. 2.4s D. 12s
A horizontal uniform meter stick supported at the 50-cm mark has a mass of 0.50 kg hanging from it at the 20-cm mark and a 0.30-kg mass hanging from it at the 60-cm mark. Determine the position on the meter stick at which one would hang a third mass of 0.60 kg to keep the meter stick balanced.
A. 74 cm B. 70 cm C. 65 cm D. 86 cm E. 62 cm
The energy needed to remove an electron from the first excited state of a Li2+ ion is
a. 53 eV b. 31 eV c. 92 eV d. 122 eV e. 61 eV
If body P, with a positive charge, is placed in contact with body Q (initially uncharged), what will be the nature of the charge left on Q?
a. must be greater in magnitude than that on P b. must be equal in magnitude to that on P c. must be negative d. must be positive