Aradioactive sample of a pure element produces 30240 decays per minute at one point in an experiment and 101.95 minutes later, produces 945 decays per minute. what is the half-life? (ii) what is the decay constant? (iii) what is the mean lifetime of the element? (b) what fraction of a sample of sodium-22 is left after 6.505 yr. (the half-life of sodium-22 is 2.602 yr.) (c) what period of time is required for a sample of radioactive carbon-14 to lose 66.667% of its activity? (the half-life of carbon-14 is 5730 yr)

The correct answer is  "c".  it is "c" because melting is an endothermic change, and endothermic get's energy from surroundings. 

Answertraveling around a circular trackexplanation"traveling around a circular track" is the best answer as you could be traveling around a circular track at a constant speed. your velocity would therefore have the same magnitude but will always be constantly direction. since acceleration is the rate of change of velocity, the rate of change will only involve the direction of velocity and not the magnitude.wrong choices: "an object at rest" does not accelerate at all"increasing speed while traveling around a curve" means that the acceleration will not be constant due to only change in direction; it will be constant due to both magnitude and direction"an object in free fall" does not necessarily change direction 

All are great precautions but you can still lift lighter and different muscles in between hard workdays. this keeps other muscles not usually used in shape.