20. Sterling Archer, despite failing repeatedly at pole-vaulting, is determined to master the skill. He is holding a vaulting po
le parallel to the ground. The pole is 5 m long. Archer grips the pole with his right hand 10 cm from the top end of the pole and with his left hand 1 m from the top end of the pole. Although the pole is quite light (its mass is only 2.5 kg), the forces that Archer must exert on the pole to maintain it in this position are quite large. How large are they? (Assume that Archer exerts only vertical—up or down—forces on the horizontal pole and that the center of gravity of the pole is located at the center of its length.)
1 answer:
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Answer:
A) 1000 joules
Explanation:
In general work is given by the equation:
(1)
A) With the displacement and
the force applied, because the force and the displacement are parallel (the crate is pushed horizontally)
is simply
, and because the path is a straight line and the force is constant work is:
(2),
B) The work-energy theorem says that the total work on a body is equal to the change on kinetic energy:
(3)
The total work on the crate is the work done by the push and plus the work of the friction (4) , as (A) because forces are parallel to the displacement
(5) and
(6), the due friction always has negative sign because is opposite to the displacement, using (6), (5) and (4) on (3):
(3)
C) The energy is lost by friction, so the amount of energy turned into heat is the work the friction does:
(3)