A Geiger counter registers a count rate of 8,000 counts per minute from a sample of a radioisotope. The count rate 24 minutes later is 1,000 counts per minute. The half life of the radioisotope is __________
Fill in the blank(s) with correct word
8 minutes
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A farsighted boy has a near point at 2.0 m and requires eyeglasses to correct his vision. Corrective lenses are available in increments in power of 0.25 diopters
The eyeglasses should have lenses of the lowest power for which the near point is no further than 25 cm. The boy borrows eyeglasses that have a power of +2.75 diopters. With these eyeglasses, the near point of the boy, in cm, is closest to: A) 31 B) 28 C) 33 D) 37 E) 40
A cube of copper 0.10 meters on each side has an average grain size of 10 × 10-6 m. The average grain boundary energy of copper is 625 × 10-3 J/m2 . Assume that all of the grains are cubes 10 × 10-6 m across.
In simple harmonic motion the position of the oscillator:
A. Is behind its acceleration by a quarter cycle, or 
radians
B. Leads its acceleration by a quarter cycle, or 
radians
C. Leads its velocity by a quarter cycle, or 
radians
D. Is behind its velocity by a quarter cycle, or 
radians
Using the observations of the Solar and Heliospheric Observatory (SOHO) and Solar Dynamics Observatory (SDO), it may be possible to predict mass ejections from the Sun days in advance
Indicate whether the statement is true or false