A small metal ball is suspended from the ceiling
by a thread of negligible mass. The ball
is then set in motion in a horizontal circle so
that the thread describes a cone.
The acceleration of gravity is 9.8 m/s^2
What is the speed of the ball when it is in
circular motion?
Answer in units of m/s.
Part 2: How long does it take Tperiod for the ball to
rotate once around the axis?
Answer in units of s.
Picture: http://imgur.com/rMu6oQn
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Answers & Comments
Verified answer
Radius of rotation = (sin 25 x 3.1) = 1.31 metres.
Centripetal force = 5.4(tan 25 x g) = 24.68 N.
V = sqrt.(fr/m) = sqrt.(24.68 x 1.31)/5.4 = 2.447 m/sec.
Circumference = (2pi r) = 8.231 metres.
(8.231/2.447) = 3.36 secs.
In this type of problem, the tension in the thread has a vertical and horizontal component. The vertical component is equal to the weight of the ball. The horizontal component is equal to the centripetal force. Since we know the angle and mass of the ball, we can use the following equation to determine the tension in the thread.
T * sin θ = m * g
Weight = 5.4 * 9.8 = 52.92 N
T * sin 25 = 52.92
T = 52.92 ÷ sin 25
This is approximately 125.2 N. Let’s determine the horizontal component of tension.
Th = T * cos θ
Th = (52.92 ÷ sin 25) * cos 25
This is approximately 113.5 N.
Fc = m * v^2 ÷ r
According the drawing, r = 3.1 * sin 25
Fc = 5.4 * v^2 ÷ (3.1 * sin 25)
5.4 * v^2 ÷ (3.1 * sin 25) = (52.92 ÷ sin 25) * cos 25
Multiply both sides by sin 25.
5.4 * v^2 ÷ 3.1 = 52.92 * cos 25
Multiply both sides by 3.1 and divide both sides by 5.4.
v^2 = 30.38 * cos 25
v = √(30.38 * cos 25)
This is approximately 5.25 m/s. The period is time for the ball to move around the base of the cone one time. The distance is equal to the circumference of a horizontal circle.
C = 2 * π * 3.1 * sin 25 = 6.2 * π * sin 25
This is approximately 8.23 meters. To determine the period, divide this distance by the ball’s velocity.
T = 6.2 * π * sin 25 ÷ √(30.38 * cos 25)
This is approximately 1.57 seconds. I hope this helps you to understand how to solve this type of problem.