2. A simple pendulum has a particle of mass m at the end of a light rod of length 1. The other end of the rod is attached to a fixed point O, at the origin of polar coordinates (r, 0). The particle is at position (r,0) with 0 = 0 corresponding to the particle being vertically below 0. (a) Use the formulae for acceleration in polar coordinates, a = ( − rė²)ŕ+ (2ŕė +rë)ê (2) to show that T = mg cos 0+mlo², and Ö 0 = -²² sin 0, 3 where T is the tension in the rod. Use the relation (02) = 200 to deduce that j2 2g cos 0 + A, 1 where A is a constant. If the particle is instantaneously at rest (0 = 0) when the rod is horizontal, find and T when the rod is vertical. How does the tension in the vertical position (which is also the maximal tension) depend on the rod's length 1? (b) Assume the particle is subject to linear air resistance -av. Use the expression of the velocity in polar coordinates v =ŕŕ+rð (3) together with (2) to write the equations of motion in polar coordinates. Show that, under the small-angle approximation sin≈ 0, the particle's position satisfies the fundamental equation of damped harmonic motion.

Algebra & Trigonometry with Analytic Geometry
13th Edition
ISBN:9781133382119
Author:Swokowski
Publisher:Swokowski
Chapter11: Topics From Analytic Geometry
Section11.5: Polar Coordinates
Problem 98E
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2. A simple pendulum has a particle of mass m at the end of a light rod of length 1. The other
end of the rod is attached to a fixed point O, at the origin of polar coordinates (r, 0). The
particle is at position (r,0) with 0 = 0 corresponding to the particle being vertically below
0.
(a) Use the formulae for acceleration in polar coordinates,
a = ( − rė²)ŕ+ (2ŕė +rë)ê
(2)
to show that
T = mg cos 0+mlo², and
Ö
0 = -²² sin 0,
3
where T is the tension in the rod. Use the relation (02) = 200 to deduce that
j2
2g
cos 0 + A,
1
where A is a constant. If the particle is instantaneously at rest (0 = 0) when the rod is
horizontal, find and T when the rod is vertical. How does the tension in the vertical
position (which is also the maximal tension) depend on the rod's length 1?
(b) Assume the particle is subject to linear air resistance -av. Use the expression of the
velocity in polar coordinates
v =ŕŕ+rð
(3)
together with (2) to write the equations of motion in polar coordinates. Show that, under
the small-angle approximation sin≈ 0, the particle's position satisfies the fundamental
equation of damped harmonic motion.
Transcribed Image Text:2. A simple pendulum has a particle of mass m at the end of a light rod of length 1. The other end of the rod is attached to a fixed point O, at the origin of polar coordinates (r, 0). The particle is at position (r,0) with 0 = 0 corresponding to the particle being vertically below 0. (a) Use the formulae for acceleration in polar coordinates, a = ( − rė²)ŕ+ (2ŕė +rë)ê (2) to show that T = mg cos 0+mlo², and Ö 0 = -²² sin 0, 3 where T is the tension in the rod. Use the relation (02) = 200 to deduce that j2 2g cos 0 + A, 1 where A is a constant. If the particle is instantaneously at rest (0 = 0) when the rod is horizontal, find and T when the rod is vertical. How does the tension in the vertical position (which is also the maximal tension) depend on the rod's length 1? (b) Assume the particle is subject to linear air resistance -av. Use the expression of the velocity in polar coordinates v =ŕŕ+rð (3) together with (2) to write the equations of motion in polar coordinates. Show that, under the small-angle approximation sin≈ 0, the particle's position satisfies the fundamental equation of damped harmonic motion.
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