A person holds a load of 2 kg in the hand, 35 cm from the elbow…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A person holds a load of kg in the hand, cm from the elbow. The biceps is attached to the forearm cm from the elbow. Treat the forearm as a lever with the elbow as the fulcrum. Take .
- What is the weight of the load?
- What force must the biceps supply to hold the load still?
- How many times larger is this force than the weight?
Need a reminder? The key ideaShow
Joints are fibrous (no movement), cartilaginous (limited) or synovial (much movement: ball and socket, hinge, pivot, gliding, saddle). Myasthenia gravis, muscular dystrophy and tetany affect muscle. Arthritis, osteoporosis and gout affect joints and bones. For a lever at rest, effort times its distance from the fulcrum equals load times its distance from the fulcrum.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Given. Load: kg at cm. Biceps at cm. .
Plan. Find the weight, then balance the moments about the elbow.
Step 1. Weight. .
Step 2. Moments. . We want , so .
Step 3. The ratio. , which is also .
Answer: N; N; times.
Check. The biceps is times nearer to the elbow than the load, so its force must be times larger.
Watch out. This is a model with round numbers. It ignores the weight of the forearm and the angle of the muscle. This lever is not in the NEET syllabus.
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