The next two questions refer to the following situation: A mass m is attached to

Question

The next two questions refer to the following situation: A mass m is attached to a rigid, massless rod of length R. The rod is pivoted at one end so the mass can swing in a vertical circle. The mass starts at the top of its are and is given an initial speed v, as shown. (Note that the initial speed is not zero!) The mass swings down through a 180degree arc and strikes a horizontal spring, which has spring constant k. The spring compresses an amount x, just stopping the mass at the bottom of its swing. What is the maximum compression x of the spring? root 1/k(mv2 + 4mgR) root 1/k(mv2 + 2mgR) root 1/k(v2 + 2gR) 2 root gmR/k None of these Which of the following forces do positive work on the mass during this process? the force of gravity the force of the spring the force of the rod i ii iii i and ii i and iii ii and iii none of these forces

Explanation / Answer

total energy initially = KE + PE = 0.5mv^2 + 2mgR
final energy = 0.5kx^2
on solving for x
x = root(mv^2 / k + 4mgR / k)
correct option is A

only the gravitational force does positive work as it is in same direction as motion of the ball....

so correct option is i

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