question archive 1)Let us say as we land at the end of a jump we use the muscles in our knees to help cushion the collision
1)Let us say as we land at the end of a jump we use the muscles in our knees to help cushion the collision
Subject:BiologyPrice: Bought3
1)Let us say as we land at the end of a jump we use the muscles in our knees to help cushion the collision. (Earlier in the class we considered a case where we ignored this potential cushioning.) The center of mass of a person of mass mb falls a distance h before the person's feet make contact with the ground, and then the person's center of mass is lowered by a distance s and the reaction force from the ground F is used to cushion the collision: By using conservation of energy, show that the required force is F = mbg(1 + h/s).
2) Some professional soccer players have the same type of loss of cognitive ability as do boxers, likely due to the repeated heading of soccer balls. What is the force experienced by the head when a 82 kg soccer player hits or redirects the ball with his/her head (a header)? Assume that the 430 g ball is moving at 50 mph and hits the head at a normal angle, so it bounces back on the original path. Say that the collision with the head is elastic and the ball is squeezed by 3 cm in the collision. Treat the collision as with the head (and not the rest of the body) and mhead = 0.081mb. Make necessary assumptions wherever needed, but provide a rationale for your assumptions.
3) In professional football, a linebacker and fullback, both weighing 245 lb, are racing toward each other running at 30 ft/s. (Actually, the linebacker is running to the fullback and the fullback is starting to run away from him.) They collide and then both decelerate at a constant rate and become stationary in 0.2 s:
(a) What is the deceleration of each? (Also express your answer in g.)
(b) What is the force on each during the collision?
4) A big defensive lineman in professional football weighing 310 lb runs at a speed of 24 ft/s into a small quarterback weighing 189 lb, who is initially still. Using conservation of linear momentum, what are their speeds after this collision and in what directions are they moving? What is theforce that the quarterback feels? Assume all frictional forces during the collision can be neglected, so kinetic energy is also conserved during the collision.
