How does the length of a string affect the number of times a pendulum will swing back and forth in 10 seconds?

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

Which two particles are found in the center of an atom

What would be the strength of earth's gravitational field at a point where an 80.0 kg astronaut would experience a 80% reduction in weight