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Ush
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Homework Statement
A particle having charge q=+2.30 µC and mass m=0.0139 kg is connected to a string that is L=1.30 m long and is tied to the pivot point P in the figure below.
[PLAIN]http://capa.physics.mcmaster.ca/figures/sb/Graph25/sb-pic2515.png
The particle, string, and pivot point all lie on a horizontal table. The particle is released from rest when the string makes an angle θ=58.8° with a uniform electric field of magnitude E=294 V/m. Determine the speed of the particle when the string is parallel to the electric field (point a in the figure).
Homework Equations
Note: These are equations I think might apply, they are no equations given specifically for this question
E = -dV/dx
F = qE
τ = rFsinθ = Iɑ
U = qV
ѡf2 = wi2 + 2ɑΘ
v = ѡr
F = force
V = voltage
E = electric field
I = moment of inertia
ɑ = angular acceleration
q = charge
τ = torque
ѡ = angular velocity
d = angular displacement
r = radius
v = velocity
The Attempt at a Solution
The question states that the system rests on top of a horizontal table. Therefore, I ignored the gravity / normal forces.
It looks like a torque question, so.
τ = rFsinθ
τ = r(qE)sinθ
τ = 7.519 x 10-4
T = Iɑ
ɑ = T/I
I = ∑miri2
I = 0139(1.3)2
ɑ = 0.032rad/s2
ѡf2 = wi2 + 2ɑΘ
ѡf2 = 2ɑΘ
ѡf2 = 2(0.032)(58.8π/180)
ѡf = 0.256rad/s
v = wr
v = 1.3(0.256)
v = 0.333m/s
the computer says this is the wrong answer =/
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