A rifle bullet with mass 8.00 g and initial horizontal velocity 280 m/s strikes and embeds itself in a block with mass 0.992 kg that rests on a frictionless surface and is attached to one end of an ideal spring. The other end of the spring is attached to the wall. The impact compresses the spring a maximum distance of 15.0 cm. After the impact, the block moves in SHM. Calculate the period of this motion.

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Answer:

0.4113772 s

Explanation:

Given the following :

Mass of bullet (m1) = 8g = 0.008kg

Initial horizontal Velocity (u1) = 280m/s

Mass of block (m2) = 0.992kg

Maxumum distance (x) = 15cm = 0.15m

Recall;

Period (T) = 2Ļ€āˆš(m/k)

According to the law of conservation of momentum : (inelastic Collison)

m1 * u1 = (m1 + m2) * v

Where v is the final Velocity of the colliding bodies

0.008 * 280 = (0.008 + 0.992) * v

2.24 = 1 * v

v = 2.24m/s

K. E = P. E

K. E = 0.5mv^2

P.E = 0.5kx^2

0.5(0.992 + 0.008)*2.24^2 = 0.5*k*(0.15)^2

0.5*1*5.0176 = 0.5*k*0.0225

2.5088 = 0.01125k

k = 2.5088 / 0.01125

k = 223.00444 N/m

Therefore,

Period (T) = 2Ļ€āˆš(m/k)

T = 2Ļ€āˆš(0.992+0.008) / 233.0444

T = 2Ļ€āˆš0.0042910

T = 2Ļ€ * 0.0655059

T = 0.4113772 s

The period of the simple harmonic motion (SHM) is 0.42 s.

The given parameters;

  • mass of the bullet, m₁ = 8 g = 0.008 kg
  • initial horizontal velocity of the bullet, u = 280 m/s
  • mass of the block, mā‚‚ = 0.992 kg
  • initial velocity of block, uā‚‚ = 0
  • extension of the spring, x = 15 cm = 0.15 m

The final velocity of the system after the impact is calculated as follows;

[tex]m_1 u_1 + m_2u_2 = v(m_1 + m_2)\\\\0.008(280) \ + \ 0.992(0) = v(0.008 \ + \ 0.992)\\\\2.24 = v(1) \\\\v = 2.24 \ m/s[/tex]

The spring constant is calculated as follows;

[tex]\frac{1}{2} kx^2 = \frac{1}{2} mv^2\\\\k = \frac{mv^2}{x^2} \\\\k = \frac{(0.008 + 0.992))\times 2.24^2}{(0.15)^2} \\\\k = 223 \ N/m[/tex]

The angular speed of the simple harmonic motion (SHM) is calculated as follows;

[tex]\omega = \sqrt{\frac{k}{m} } \\\\\omega = \sqrt{\frac{223}{(0.008 + 0.992)} }\\\\\omega = 14.933 \ rad/s[/tex]

The period of the oscillation is calculated as follows;

[tex]T = \frac{2\pi }{\omega} \\\\T = \frac{2\pi }{14.933} \\\\T = 0.42 \ s[/tex]

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