two friends are talking to another person across the building the other person can hear them but not see them why is this?

Astudent pushes on a 20.0 kg box with a force of 50 n at an angle of 30° below the horizontal. the box accelerates at a rate of 0.5 m/s2 across a horizontal floor. what is the value of the normal force on the box? 200 n 243 n 156 n 225 n

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

The frequency of the fundamental of the guitar string is 320 hz. at what speed v do waves move along that string?