True or False:
Less power is required while lifting a box up quickly than while slowly lifting it.
A source of energy is required to do work.
Without friction or work by an external force, the sum of the potential and kinetic energies of a body is constant.
Work cannot be done in the absence of motion.
Energy conservation law for a projectile (no friction): Potential energy increase equals the kinetic energy decrease.
Work is done when the form of energy changes.

Explain vector addition, triangle method and parallelogram method

If the chemical properties of a substance remain unchanged and appearance or shape of a substance changes it is called a ?

Electric field of the earth. the earth has a net electric charge that causes a field at points near its surface equal to 150 n> c and directed in toward the center of the earth. (a) what magnitude and sign of charge would a 60-kg human have to acquire to overcome his or her weight by the force exerted by the earth’s electric field? (b) what would be the force of repulsion between two people each with the charge calculated in part (a) and separated by a distance of 100 m? is use of the earth’s electric field a feasible means of flight? why or why not?