Daredevil Darla has heard that to avoid injury when jumping out of her rocket she should bend her knees upon landing. Darla has a mass of 74 kg. If just before contact with the ground, she has a downward speed of 7.3 m/s, then. . .   (a) In a stiff -legged landing she comes to a halt in 2.0 ms. Find the average net force that acts on her during this time. (   b) When she bends her knees, Darla comes to a halt in 0.10 s. Find the average net force now.   (c) During the landing, there are two forces acting on Darla: the normal force from the ground points upward, while her weight force points downward. The average net force acting on Darla includes both of these forces. Taking into account the directions of the forces, find the force of the ground on Darla in parts (a) and (b).

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Newton’s Third Law of Motion

The horse pulls the cart and the cart pulls the horse in response as per Newton third law. So the big question is, “Don’t the two forces cancel each other? How does the cart accelerate?”