If chromium-51 goes 4 half-lives and has been decaying for 240 days how long is one half-life?​

The image shows a pendulum in simple harmonic motion the pendulum starts at a and swing to e

Students design a model roller-coaster track. they place a rubber ball at the highest point on the track and let it go. the ball rolls along the track pulled only by the force of gravity. eventually, it comes to a stop. which change to the design will result in the ball moving the greatest distance?

What is the single most important equation in all of physics?