A Hospital patient has injured her leg, how much mass must be used to keep her leg stationary.  The leg has a mass of 2.6 kg and is 0.87 meters in length, the rope for the tension mass  is connected at 0.65 meters from the knee.

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Interesting, I just answered some of these posted later under different names.

To determine the mass needed to keep the patient's leg stationary, we need to consider the torque acting on the leg. The torque is the product of the force applied and the distance from the axis of rotation.

In this case, the force is the tension in the rope pulling upward, and the distance is the distance from the knee where the rope is connected.

First, let's calculate the torque exerted by the leg itself. The torque exerted by an object can be calculated using the formula torque = force × distance. In this case, the distance is the length of the leg (0.87 m) and the force is the gravitational force acting on the leg.

The gravitational force exerted on the leg can be calculated using the formula force = mass × gravitational acceleration. The mass of the leg is given as 2.6 kg, and the gravitational acceleration is approximately 9.8 m/s^2.

So, the torque exerted by the leg can be calculated as follows:
torque_leg = force_leg × distance_leg
= (mass_leg × gravitational acceleration) × distance_leg
= (2.6 kg × 9.8 m/s^2) × 0.87 m

Next, let's calculate the torque exerted by the tension mass. Since the leg is stationary, the torque exerted by the tension mass must balance out the torque exerted by the leg. The distance for the tension mass is given as 0.65 m.

The torque exerted by the tension mass can be calculated using the formula torque_tension = force_tension × distance_tension.

Since the leg is stationary, the torque exerted by the tension mass must be equal to the torque exerted by the leg. Therefore, we can set up the equation as follows:
torque_leg = torque_tension
(mass_leg × gravitational acceleration) × distance_leg = force_tension × distance_tension

Now, we can solve for the force_tension by rearranging the equation:
force_tension = (mass_leg × gravitational acceleration × distance_leg) / distance_tension

Finally, to find the mass that corresponds to this force, we can use the formula force = mass × gravitational acceleration and rearrange it to solve for mass:
mass_tension = force_tension / gravitational acceleration

So, the formula to find the mass needed to keep the patient's leg stationary is:
mass_tension = ((mass_leg × gravitational acceleration × distance_leg) / distance_tension) / gravitational acceleration

Plugging in the given values, we can calculate the mass needed to keep the leg stationary.