Question
A 0.14 kg pinecone falls 16 m to the ground, where it lands with a speed of 13 m/s. With what speed would the pinecone have landed if there had been no air resistance? Did air resistance do positive work, negative work, or zero work on the pinecone?
Answer
Potential energy at top = kinetic energy at the ground
=> mgh = (0.5) mv^2
=> v = √(2gh) = √(2 * 9.8 * 16) = 17.70 m/s.
Work done by air resistance is negative as the force and displacement are in opposite directions. In other words, work done by pinecone on air is positive and hence it loses kinetic energy equal to the work done.
Hence, work done by air resistance
= - (0.5) *(0.14) [ (17.7)^2 - (13)^2]
= -10.1 J
If F = average force, then
F * 16 = 10.1
=> F = 10.1/16 = 0.63 N.
A 0.14 kg pinecone falls 16 m to the ground, where it lands with a speed of 13 m/s. With what speed would the pinecone have landed if there had been no air resistance? Did air resistance do positive work, negative work, or zero work on the pinecone?
Answer
Potential energy at top = kinetic energy at the ground
=> mgh = (0.5) mv^2
=> v = √(2gh) = √(2 * 9.8 * 16) = 17.70 m/s.
Work done by air resistance is negative as the force and displacement are in opposite directions. In other words, work done by pinecone on air is positive and hence it loses kinetic energy equal to the work done.
Hence, work done by air resistance
= - (0.5) *(0.14) [ (17.7)^2 - (13)^2]
= -10.1 J
If F = average force, then
F * 16 = 10.1
=> F = 10.1/16 = 0.63 N.
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