A10 kg backpack is on the floor. someone gently pulls on it, upwards with a 15 n force. what is the normal force acting on the backpack?

If backpack was simply at rest then normal force would be 100N( g=10m/s^2). It's is being pulled gently in upward direction. So Normal force will be. N= mg - 15 = 10x10 - 15 = 85N. I took g=10m/s^2 for simplification. Hope it helps.

1) when you rub your hands together quickly, the kinetic energy is converted to mechanical energy.2) thermal energy from the sun travels to earth as infrared waves.3) energy is transferred through the matter of space by electromagnetic waves. 4) when a match is burned, chemical potential energy is converted to thermal and radiant energy. 5) seismicwaves are caused by back and forth movement , or vibration, of an object. 6) mechanicalenergy in an engine changes thermal energy into kinetic energy to make a car move.