Q1. To give a 19kg child a ride, two teenagers pull on a 4kg sled with ropes, as indicated in the figure. Both teenagers pull with a force of F = 55N at the angle of 35° relative to the forward direction, which is the direction of motion. In adding, the snow exerts a retarding force on the sled that points opposite to the direction of motion, and has a magnitude of 57 N. Find out the acceleration of the sled and child.

Q2. A nursing mother puts her baby to her breast every time she hears it cry. After a few days, her milk starts to flow once she hears the baby cry. In terms of classical conditioning, what is the conditioned stimulus?