Astudent gets in an elevator and sets her backpack of mass m on the floor. the elevator accelerates upward with an acceleration a. (a) what is the normal force on her backpack? (b) now, she gives the backpack a kick, so that it has a speed v. it comes to rest a distance l from where it started. find the coefficient of kinetic friction between the backpack and the floor.

the aurora is formed when charged particles emitted from the sun during a solar flare penetrate the earth's magnetic shield and collide with atoms and molecules in our atmosphere. these collisions result in countless little bursts of light, called photons, which make up the aurora.

auroras are generated by charged solar particles hitting molecules in earth's atmosphere. this usually happens in high latitudes, because our planet’s magnetic field tends to funnel these particles toward the poles. that’s why it can be experienced in northern ohio.