the pan spiring balance has mass of 300g. when suspended from the coil spring it is found to stretch the spring 10cm. a lump of putty of mass 200g si dropped from rest onto the pan from the height of 30cm. find the maximum distance the pan moves downward
Answers
Answer:
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Given:
Mass of pan (m₁) = 300 g = 0.3 kg
Mass of putty (m₂) = 200 g = 0.2 kg
Spring extended (x₀) = 10 cm = 0.1 m
Height from which putty was dropped (h) = 30 cm = 0.3 m
To find:
The maximum distance the pan moves downward.
Solution:
Previously when pan was suspended, then mass spring system was balanced.
So, Spring force Fs = kx₀
Gravity force = mg
kx₀ = m₁g
k = m₁g/x₀
k = (0.3)(9.8)/0.1
k = 29.4 N/m
Now when putty was dropped, then when it falls on pan, its initial velocity = v₀
From equation: v₀² = u₀² + 2gh
v₀² = 0 + 2(9.8)(0.3)
v₀ = 2.425 m/s
Initial velocity of pan = 0
Now putty and pan move together with final velocity = vf
From conservation of momentum
pi = pf
m₂v₀ = (m₁ + m₂)vf
vf = m₂v₀/(m₁ + m₂)
vf = (0.2)(2.425)/(0.3 + 0.2)
vf = 0.97 m/s
So, at x = x₀
Kinetic energy of system Ki = (1/2)(m₁ + m₂)vf²
Potential energy of the system Vg = (m₁ + m₂)g(x_max - x₀)
at x = x₀, potential energy in the spring
Vsi = (1/2)kx₀²
Now at x = x_max, potential energy of the spring
Vsf = (1/2)kx_max²
Gravitational potential energy, Ugf = 0
Final kinetic energy, Kf = 0
So, from energy conservation
Ki + Ug + Usi = Kf + Ugf + Usf
1/2(m₁ + m₂)vf² + (m₁ + m₂)g(x_max - x₀) + (1/2)kx₀² = (1/2)kx_max²
(0.5 × 0.97²) + (1 × 9.8)(x_max - 0.1) + (29.4 × 0.1²) = 29.4 × x_max²
0.47045 + 9.8x_max - 0.98 + 0.294 = 29.4 × x_max²
-0.21555 + 9.8 x_max = 29.4 x_max²
29.4 x_max² - 9.8 x_max + 0.21555 = 0
x_max = 0.31 , 0.023
So, x_max = 0.31 m
If, consider 0.21555 ≈ 0
Then, 29.4 x_max² - 9.8 x_max = 0
x_max(29.4 x_max - 9.8) = 0
x_max = 0
Or, 29.4 x_max - 9.8 = 0
29.4 x_max = 9.8
x_max = 9.8 / 29.4
So, x_max = 3.33 m