Final answer:
The source of energy that moves the wagon when Sam pulls his sister over a flat sidewalk is the chemical energy in Sam's muscles, which gets converted to mechanical energy.
Step-by-step explanation:
The source of energy that moves the wagon when Sam pulls his sister in it on a flat sidewalk is the Chemical energy in Sam's muscles. This energy is stored in the molecules that make up the food Sam eats. When he exercises his muscles to pull the wagon, this stored chemical energy is converted to Mechanical energy.
The source of energy that moves the wagon when Sam pulls his sister in it on a flat sidewalk is A) Chemical energy in Sam's muscles. When Sam's muscles contract, they release chemical energy that is converted into mechanical energy, allowing him to pull the wagon and his sister. This mechanical energy is then transferred to the wagon, causing it to move.
Essentially, Sam's muscles are doing work on the wagon as he pulls it along. Sam is exerting a force parallel to the displacement of the wagon, causing it to move. This demonstrates the transfer of energy from Sam (the system) to the wagon (the external environment).
While the kinetic energy of the rolling wheels, potential energy from the ground and gravitational energy pulling on the wagon have roles in movement, they're not energy sources. They are forms of energy the wagon possesses or can access, but Sam's muscles are providing the energy to initiate and maintain the motion.
Learn more about Energy transfer