Solve Physics Problem: Help a Student Lift Weight

[Woody11]

This is the last question I will as for help on for this assignment I am doing I promise. For all you out there who know Physics you are awesome, cause boy is this stuff hard. Here is the question I am have trouble with now, again this could be an easy question but I am not sure on what to do. I have been trying to figure it out but no way can I do it.

A student is trying to life a weight held in the hand. The distance from the elbow joint to the centre of gravity of the weight they are trying to life is 30cm. Their flexor muscles of the forearm insert 5cm from the centre of rotation of the elbow joint (the pivot). If the tendon inserts into the bone at an angle of 20 degrees, and the muscle is able to generate 40 kilograms of internal tension; How much weight could the student lift??

I hate to be bothering for help but this assignment I am doing is worth 20% and I am hoping to do well, the rest of teh questions on this part I think I can handle. If someone could help me with this one it would be great.

Thanks,Woody

 

[Touchkin]

The student can lift (slowly) the weight while the torque (of the hand around the centre of rotation of the elbow joint) that is created by the tendon, which balances the torque created by the weight, is less then the value corresponding to the maximum force that the muscle can generate.

To evaluate the maximum weight the hand we are talking about can lift we've got to write the equation of the torques around the elbow joint (it is the pivot) for the critical case:

m*30=40*sin(20*)*5

Solve it and get the answer;

And take it easy!

 

[thepatientmental]

Hi Woody,

No need to apologize for asking for help, we all need assistance sometimes! Let's break down the problem step by step.

First, we need to understand the concept of torque. Torque is a measure of rotational force and is calculated by multiplying the force applied by the distance from the pivot point. In this case, the pivot point is the elbow joint and the weight is being held at a distance of 30cm from it.

Next, we need to consider the angle at which the flexor muscle inserts into the bone. This angle affects the amount of torque that can be generated by the muscle. We can use the formula Torque = Force x Distance x sin(angle) to calculate the maximum torque that can be generated by the muscle.

Now, we know that the muscle is able to generate 40 kilograms of internal tension. We can convert this to Newtons, the standard unit of force in physics, by multiplying it by the acceleration due to gravity (9.8 m/s^2). This gives us a force of 392 N.

Plugging in the values to the torque formula, we get:

Torque = 392 N x 5 cm x sin(20 degrees)
= 392 N x 0.08716
= 34.2 Nm

This is the maximum torque that the muscle can generate. To find the maximum weight that the student can lift, we need to divide this torque by the distance from the elbow joint to the centre of gravity of the weight (30cm). This gives us:

Weight = 34.2 Nm / 30 cm
= 1.14 N

So, the maximum weight that the student can lift is approximately 1.14 kg. Keep in mind that this is assuming ideal conditions and does not take into account factors such as fatigue or the weight of the student's arm.

I hope this helps and good luck with your assignment! Remember, practice makes perfect and don't hesitate to ask for help when you need it. Physics can be tough, but with perseverance, you can master it.