which of the following represents work: A compressed spring that is allowed to expand. The normal force on a stationary crate. The frictional force on a crate that is being pushed across a flat floor. The weight of a ball that rolls, without slipping, on a flat surface. A stretched spring that is allowed to contract. The reaction force on a pin support. The weight of a ball that rolls, without slipping, down a ramp. The frictional force on a crate sliding down a ramp.