Students were asked to write a response as to how energy is used when driving a car. Their responses are written below. Student 1: Energy is used to stop a car. Student 2: Energy is used to turn a car. Student 3: Energy is used to cause a car to go faster. Student 4: Energy is used to allow a car to move in a straight line. Which student’s response is least likely indicating a change in motion?

Radon-222 or rn-222 has a half-life of 3.82 days. to determine the fraction of an original sample of rn-222 that remains unchanged after 7.646 days, we calculate the amount of rn-222 remaining after 7.646 days and divide it with the original amount. using 1 gram as a basis and using half-life calculation methods, we can determine that  0.249 or 0.25  grams of rn-222 will remain, and thus the fraction remaining is 0.25 or 1/4.