What is the definition of the half-life of a radioactive isotope? A. The time it takes for half the parent nuclei in a sample to become
daughter nuclei
B. The time it takes for all the parent nuclei in a sample to become
daughter nuclei
C. The time it takes for all the daughter nuclei in a sarnple to become
parent nuclei
D. The time it takes for half the daughter nuclei in a sample to
become parent nuclei

Given the position vector of the particle r(t)=(t+1)i+(t^2−1)j+2t k, find the particle's velocity and acceleration vectors at t=1

(**i would really appreciate if this was answered soon** ) which pair of quantities includes one quantity that increases as the other decreases during simple harmonic motion?

Two students, each riding bicycles, start from the same apartment building and ride to the same building on campus, but each takes a different route. the first student rides 1100 m due east and then turns due north and travels another 1430 m before arriving at the destination. the second student heads due north for 1930 m and then turns and heads directly toward the destination.at the turning point, how far is the second student from the destination?