5.The elastic energy stored in your tendons can contribute up to 35 % of your en

Question

5.The elastic energy stored in your tendons can contribute up to 35 % of your energy needs when running. Sports scientists have studied the change in length of the knee extensor tendon in sprinters and nonathletes. They find (on average) that the sprinters' tendons stretch 42 mm , while nonathletes' stretch only 33 mm .

question : The spring constant for the tendon is the same for both groups, 31 N/mm . What is the difference in maximum stored energy between the sprinters and the nonathletes?

3.How fast would a(n) 73 kg man need to run in order to have the same kinetic energy as an 8.0 g bullet fired at 410 m/s ?

Explanation / Answer

solution:

2)

31N/mm = 31,000N/m and elastic potential energy is given by:

PE(s) = 0.5kx²

For the sprinters, the maximum average stored energy is;

PE(s) = 0.5(31,000N/m)(0.042m)²
= 27.342J

For non-athletes it’s:

PE(s) = 0.5(31,000N/m)(0.033m)²
= 16.88J

A difference of 10.46Joules.

3) K.E.=1/2mv2

Bullet KE =man KE

1/2mbulletv2 =1/2mman v2

8*10-3*(4102) =73*v2

vman = 4.3 m/s ans

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