This question is from Physics, Walker, 4th E, CH 8, question 34. the question in

Question

This question is from Physics, Walker, 4th E, CH 8, question 34.

the question involves a pendulum which swings through it's lowest point to a point A, and 35 degrees off of straight down. I got the first few parts of the question right.

The final part of the question asks about change in speed at point A if the pendulum's mass were increased. The chegg answer states that speed at point A is increased if the mass of the pendulum is increased. This defies my understanding of the way that gravitational force works. Since gravity makes things fall with the same acceleration, shouldn't it slow a pendulum on its upswing at the same rate, regardless of mass? And if not, why?

Explanation / Answer

Applying energy conservation,

total energy at A = total energy at B

m g L(1 - cos35) + 0 = 0 + m v^2 /2

v^2 = 2 g L (1 - cos(theta))

v = sqrt[2 g L (1 - cos(theta)) ]

v is independent of mass hence it stays same. ......Ans(D)

{ but for Part C, change in gravitational PE = m g deltaH , it will increase if mass is increased.}

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