Question

You are pushing against the ground as you begin to leap into the air (but you are still in contact with the ground). (a) Are you accelerating as you begin your leap? Choose one answer only. No, you are not accelerating. Yes, you are accelerating upward. Yes, you are accelerating downward. Incorrect: Your answer is incorrect. (b) What is the net force acting on you as you begin your leap? Choose one answer only. The net force acting on you is zero. The net force acting on you is upward. The net force acting on you is downward. Incorrect: Your answer is incorrect. (c) Compare the normal force exerted on you by the ground to the gravitational force exerted on you by the earth (your weight). Choose one answer only. The normal force from the ground is smaller than your weight. The normal force from the ground is greater than your weight. The normal force from the ground is equal to your weight. Incorrect: Your answer is incorrect.

Answer 1

When a person is standstill it exerts the force on the ground similar to its weight (mass * g). And according to the Newton's third law, ground also exerts equal force in opposite direction to balance it.

Now in the process of vertical jumping, initially the person bends his knees, swings his arms and prepares the jump by lowering the center of gravity. The following curve shows all three phases of vertical jumping.

The force-time graph shows that the athlete reaches peak forces shortly after reaching the lowest point of the jump. He then further accelerates until his feet leave the ground.

Therefore we can clearly see that :-

The person is accelerating upward as he begins his leap.

The Net force acting on the person is upward (that's why acceleration is upward)

Because Net force is upward, it means Normal force from the ground is heigher than the weight of the person.