What is the time tb it will take for point b of the wavefront to encounter the vacuum/material interface? note that you will express your answer in a slightly unusual way. express your answer numerically in units of t1 (the time it takes light to travel a distance d in a vacuum). use three significant figures. view available hint(s)

As part of your daily workout, you lie on your back and push with your feet against a platform attached to two stiff springs arranged side by side so that they are parallel to each other. when you push the platform, you compress the springs. you do an amount of work of 79.0 j when you compress the springs a distance of 0.230 m from their uncompressed length. (a) what magnitude of force must you apply to hold the platform in this position? (b)how much additional work must you do to move the platform a distance 0.230 m farther? (c) what maximum force must you apply to move the platform a distance 0.230 m farther?

Avoltaic cell converts chemical energy to

In a classical model of the hydrogen atom, the electron moves around the proton in a circular orbit of radius 0.053 nm. what is the electron's orbital frequency? what is the effective current of the electron?