A crate of toys remains at rest on a sleigh as the sleigh is pulled up a hill with an increasing speed. The crate is not fastened down to the sleigh. What force is responsible for the crate’s increase in speed up the hill?
Answer Choices
A. the force of static friction of the sleigh on the crate
B. the contact force (normal force) of the ground on the sleigh
C. the contact force (normal force) of the sleigh on the crate
D. the gravitational force acting on the sleigh
E. no force is needed