linear kinetics

Question

4. A basketball player with a body weight of 850 N exerts a force of -4500 N against the ground during takeoff (jumping upward). The basketball player’s average horizontal velocity was 10m/s during the takeoff period. The basketball player’s foot was in contact with the ground for 0.5 s during the takeoff period. How much force does the ground exert on the basketball player (ground reaction force) during the takeoff period? 

Answer 1

Is this question worded correctly?  By Newton's 3rd law, the force that the ground exerts on the player must be equal and opposite to the force that the player exerts on the ground.  If the player exerts -4500 N on the ground during the jump, then the ground exerts +4500 N on the player during the jump.  I think what you really need to find here is the impulse that the ground imparts to the player.

 

I = FΔt

 

If the force of 4500 N was applied during the contact time of 0.5 s, the impulse is

 

I = (4500 N)(0.5 s) = 2250 Ns