An athlete at the gym holds a 4.33 kg steel ball in his hand. His arm is 68.7 cm long and has a mass of 4.69 kg. What is the magnitude of the torque about his shoulder if he holds his arm straight out to his side, parallel to the floor?
Torque = massball x length + massarm x length/2
= 4.33 kg x 0.687 m + 4.69 kg x 0.687 m/2
= 7.66472 x 1.374
= 10.5 N
Why is my answer incorrect?
ooops. Masses need to be multiplied by g, to get FORCE.
Your calculation for the torque is incorrect. In order to calculate the torque correctly, you need to consider the fact that the weight of both the steel ball and the athlete's arm contribute to the torque. The correct formula for torque is:
Torque = (massball x g x length) + (massarm x g x length/2)
where g is the acceleration due to gravity (approximately 9.8 m/s^2).
Let's calculate the torque using the given values:
Torque = (4.33 kg x 9.8 m/s^2 x 0.687 m) + (4.69 kg x 9.8 m/s^2 x 0.687 m/2)
= 28.39 Nm + 14.73 Nm
= 43.12 Nm
So, the correct magnitude of the torque about the shoulder is 43.12 Nm.