The half-life for an 80-gram sample of an unknown radioactive element is 5 days. How much of the unknown radioactive element remains after 10 days have passed?

A. 20 g

B. 40 g

C. 70 g

D. 80 g
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In a system with only a single force acting upon a body, what is the relationship between the change in kinetic energy and the work done by the force? answers: work is equal to the change in kinetic energy.work depends on the square of the change in potential energy.work is equal to the negative of the change in kinetic energy.work is equal to the square of the change in kinetic energy