1) Is it possible to make the right end of the rod push down by pulling on the l
ID: 1261523 • Letter: 1
Question
1) Is it possible to make the right end of the rod push down by pulling on the left end of the rod? Show on the diagram the direction that you would pull on the left end of the rod, and explain.
2) Suppose the length of your forearm is 34 cm, and its mass is 1.3 kg. If your biceps inserts into the forearm 3.5 cm from the pivot and your biceps muscle can produce a force of 800 N, how much weight can you curl? Model your forearm as a uniform rod.
1) Is it possible to make the right end of the rod push down by pulling on the left end of the rod? Show on the diagram the direction that you would pull on the left end of the rod, and explain. 2) Suppose the length of your forearm is 34 cm, and its mass is 1.3 kg. If your biceps inserts into the forearm 3.5 cm from the pivot and your biceps muscle can produce a force of 800 N, how much weight can you curl? Model your forearm as a uniform rod.Explanation / Answer
1)
If a force is applied pointing to the left to a point near the left upper end of the rod, that would tend to make the lower end of the rod press upwards.
To make the lower end of the rod press downwards, just do the opposite, and apply a force pointing to the right to a point near the left upper end of the rod.
That is a little bit subtle so that is probably what they want you to see here.
If there is a force pressing to the right on the left end of the rod, and a force pushing downwards on the right end of the rod, then the torque forces may cancel out so the rod would not spin, but there would be a resultant force on the fulcrum point at the center of the rod. The three forces together would add up to zero, taken as vectors
2)
Force: F = 800 N
Force arm: df = 3.5 cm
Forearm weight: W1 = 1.3 kg
W1 arm: d1 = 34/2 = 17 cm
Weight to be lifted: W2, to be determined
W2 arm: d2 = 34 cm
At equilibrium:
F df = W1 d1 + W2 d2
W2 = (F df - W1 d1) / d2 = (800x3.5 - 1.3x17) / 34 = 82 N
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