What do we mean by the half-life of a radioactive isotope?
A) it is the amount of time a person can be exposed to radiation without getting sick
B) it is the time for half the number of radioactive nuclei to become stable nuclei
C) it is the amount of time for half of the nuclei to become radioactive
D) it is the time for half the number of radioactive nuclei to decay
D
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A 60 kg boy standing on a skateboard with frictionless wheels and negligible mass throws a 3 kg ball straight up with a speed of 4 m/s. If the boy was at rest before the throw, his speed after the throw will be ________.
Fill in the blank(s) with the appropriate word(s).
A 10-kg object is dropped from rest. After falling a distance of 50 m, it has a speed of 26 m/s. What is the change in mechanical energy caused by the dissipative (air) resistive force on the object during this descent?
A. ?1.3 kJ B. ?1.5 kJ C. ?1.8 kJ D. ?2.0 kJ E. ?2.3 kJ
About what is the smallest mass a newborn star can have?
A) 0.01 times the mass of the Sun B) 0.08 times the mass of the Sun C) 0.8 times the mass of the Sun D) the mass of the Sun E) twice the mass of the Sun
How are we able to determine the chemical composition and temperature of any visible object?
What will be an ideal response?