Abook falls off a desk. the book has a mass of 1.2 kg and was at a height of 0.9 m. how much mechanical energy does the book have just before it hits the ground? (assume there is no air resistance.

The book's potential energy will be converted entirely to kinetic energy at that point in the fall, since we can neglect losses due to air resistance. The potential energy is given by PE=mgh, where m=1.2kg, h=0.9m, and g=9.81m/s^2. This is the acceleration due to gravity.
This gives:
PE=1.2*0.9*9.81=10.59J
This is also the kinetic (mechanical) energy right before the landing.

The car would move to the right with 150 n of force. the 150 n of force from friction and air resistance slows the car from moving to the right with 300 n of force.

Scissors and a seesaw both cut things that’s the only comparison