Question

In the act of walking, the arms swing back and forth through an angle of 45◦ each second. calculate the average force on the shoulder due to the centrifugal force. The mass of the person is 70 kg, and the length of the arm is 90 cm. Assume that the total mass of the arms is located at the midpoint of the arm.

Fraction of body weight

Head and neck 0.07 -Trunk 0.43 -Upper arms 0.07 -Forearms and hands 0.06 -Thighs 0.23 -Legs and feet 0.14 -Total 1.00

and...

Calculate the maximum velocity and acceleration of the foot of a runner who does a 100-m dash in 10 sec. Assume that the length of a step is 1m and that the length of the leg is 90cm and the center of mass is at mid-length.

Answer 1

45^o = /4 radians so angular velocity = /4 rad/s

mass = (0.07 + 0.06)70 kg = 9.1 kg

radius is distance of shoulder from mid point which is 90/2 = 45cm = 0.45m

Centifugal force is given by

The Runner starts vith velocity u = 0 and covers distance S = 100 m in time t = 10 s.

So

or acceleration

Final velocity is