Question

1. High-impact activities such as jogging can cause considerable damage to the cartilage at the knee joints. Peak loads on each knee can be eight times body weight during jogging. The bones at the knee are separated by cartilage called the medial and lateral meniscus. Although it varies considerably, the force at impact acts over approximately 11cm2 of this cartilage. Human cartilage has a Young's modulus of about 25 MPa (although that also varies).

a.) By what percent does the peak load impact of jogging compress the knee cartilage of a 73 kgkg person? Express your answer to the nearest integer.

b.) What would be the percentage for a lower-impact activity, such as power walking, for which the peak load is about four times body weight? Express your answer to the nearest integer.

2. In order to study the long-term effects of weightlessness, astronauts in space must be weighed (or at least "massed"). One way in which this is done is to seat them in a chair of known mass attached to a spring of known force constant and measure the period of the oscillations of this system. The 34.8 kg chair alone oscillates with a period of 1.45 s , and the period with the astronaut sitting in the chair is 2.25 s .

a.) Find the force constant of the spring.

b.) Find the mass of the astronaut.

Answer 1