A cylinder is fitted with a piston, beneath which is a spring, as in the drawing. The cylinder is open to the air at the top. Friction is absent. The spring constant of the spring is 3600 N/m. The piston has a negligible mass and a radius of 0.028 m. (a) When the air beneath the piston is completely pumped out, how much does the atmospheric pressure cause the spring to compress? (b) How much work does the atmospheric pressure do in compressing the spring?

Respuesta :

Answer:

a) 0.0693 m

b) Work done = 8.644 J

Explanation:

Given:

Spring constant, k = 3600 N/m

Radius of the piston, r = 0.028 m

Now, we know that the atmospheric pressure at STP = 1.01325 × 10⁵ Pa  = 101325 Pa

Now,

The force ([tex]F_P[/tex]) due to the atmospheric pressure on the piston will be:

[tex]F_P[/tex] = Pressure × Area of the piston

on substituting the values we get,

[tex]F_P[/tex] = 101325 × πr²

F = 101325 × π × (0.028)² = 249.56 N

also,

Force on spring is given as:

F = kx

where,

x is the displacement in the spring

 on substituting the values we get,

 249.56 N = 3600N/m × x

or

x = 0.0693 m

thus, the compression in the spring will be = 0.0693 m

b) Applying the concept of conservation of energy

we have,

Work done by the atmospheric pressure in compressing the spring = Potential energy gained  by the spring

mathematically,

[tex]W = \frac{1}{2}kx^2[/tex]

 on substituting the values we get,

[tex]W = \frac{1}{2}\times 3600\times (0.0693)^2[/tex]

W = 8.644 J

a) x = 0.0693 m

b) W = 8.644 J

Given :

Spring constant, K = 3600 N/m

Radius of the piston, r = 0.028 m

Solution :

Now the atmospheric pressure at STP = 1.01325 × 10⁵ Pa  = 101325 Pa

Force due to the atmospheric pressure on the piston is,

Force = Pressure × Area of the piston

on substituting the values we get,

[tex]\rm F_P = 101325\times \pi r^2[/tex]

[tex]\rm F_P = 249.56\;N[/tex]

a) We know that the force on spring is given by,

F = Kx

where, k is spring constant and x is the displacement in the spring.

[tex]249.56 = 3600\times x[/tex]

[tex]\rm x = 0.0693\;m[/tex]

b) We know that the Work Done is given by,

[tex]\rm W= \dfrac{1}{2} k x^2[/tex]

[tex]\rm W = 0.5\times 3600\times (0.0693)^2[/tex]

W = 8.644 J

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