Mechanics 3 SHMWatch

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Thread starter 14 years ago
#1
Hey, i have done the part of this exercise but as exercises do they got harded and i am stuck half way through could any please help me out with these 2 questions? Help would be greatly appreciated A) A particle is moving in a straight line with SHM of period 2pi secs about a centre O. When the particle is 0.5m from O its speed in zero. Calculate the maximum speed of the particle and its speed when it is 0.25m from O.

question 2
A piston of mass 1.5kg is moving with shm inside a cylinder. It performs 20 complete oscilations per minute and the distance between the extreme points of its motion is 2m. Calculate the maximum value of the kinetic energy possesed by the piston during its motion, stating clearly any assumptions you have made about the piston in order to calculate this.

Thanks for any help
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14 years ago
#2
A) A particle is moving in a straight line with SHM of period 2pi secs about a centre O. When the particle is 0.5m from O its speed in zero. Calculate the maximum speed of the particle and its speed when it is 0.25m from O.
Period = 2pi = 2pi/w.
Hence w=1.
v=0 at x=0.5m. Hence the amplitude is 0.5m.

Vmax at x=0:
v^2 = w^2(a^2 - x^2)
v^2 = 1(.5^2 - 0)
v = 0.5ms^-1

V at x=0.25
v^2 = 1(.5^2 - 0.25^2)
0
14 years ago
#3
A piston of mass 1.5kg is moving with shm inside a cylinder. It performs 20 complete oscilations per minute and the distance between the extreme points of its motion is 2m. Calculate the maximum value of the kinetic energy possesed by the piston during its motion, stating clearly any assumptions you have made about the piston in order to calculate this.
20 oscillations per 60 sec
1 oscillation per 3 sec.
Period = 3sec
2pi/w = 3
w = 2pi/3

Amplitude = 2/2 = 1m.

Ke max = 0.5m(vmax)^2

(Vmax)^2 = (2pi/3)^2[1 - 0^2]
Vmax = 2pi/3

Ke max = 0.75[2pi/3]^2

Assumptions: There are no resistances to the movement of the piston and it is small so can be modelled as a particle.
0
14 years ago
#4
1.
When speed is zero, distance is maximum, so amplitude(A)=0.5 m

Maximum speed is when the particle is at the center, i.e. when x=0.
v²=w²(A²-x²), when x=0 => v²=w²A², so:
Max speed = wA = 0.5 m/s

Speed @ x=0.25 can be found using:
v²=w²(A²-x²)

2.
1 oscillation is 2pi, 1 minute is 60 s => 20 osc/min = 20(2pi/60) = 2pi/3 rad/s = w
Extereme points of motion are 2m apart, so amplitude = 1m.
Maximum kinetic energy occurs when speed is maximum, so:
max speed = wA = 2pi/3 m/s
max KE = 0.5mv² = 0.5(1.5)(2pi/3)² =~ 3.29 J

Piston was modelled as a particle.
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