Babs and Buster are dragging a rock with a mass of 50 kg across the ground. Babs pulls with a force of 200 N to the left and Buster pulls with 250 N in the same direction. There is friction of 400 N opposing their pull. Plucky comes along and decides to pull the rock in the opposite direction to Babs and Buster. Plucky pulls the rock with 50 N of force.
a) What is the acceleration of the rock?