contestada

A block with mass m =6.9 kg is hung from a vertical spring. When the mass hangs in equilibrium, the spring stretches x = 0.29 m.
While at this equilibrium position, the mass is then given an initial push downward at v = 4.1 m/s. The block oscillates on the spring without friction.

1)What is the spring constant of the spring?

2)What is the oscillation frequency?

3)After t = 0.42 s what is the speed of the block?

4)What is the magnitude of the maximum acceleration of the block?

5)At t = 0.42 s what is the magnitude of the net force on the block?

Respuesta :

1) The spring constant is 233.2 N/m

2) The oscillation frequency is 0.93 Hz

3) The speed of the block is 3.2 m/s

4) The maximum acceleration is [tex]23.9 m/s^2[/tex]

5) The net force on the block is 104.9 N

Explanation:

1)

At equilibrium, the weight of the mass is equal to the restoring force of the spring. Therefore, we can write:

[tex]mg=kx[/tex]

where

m = 6.9 kg is the mass hanging on the spring

[tex]g=9.8 m/s^2[/tex] is the acceleration of gravity

k is the spring constant

x = 0.29 m is the stretching of the spring

Solving for k, we find

[tex]k=\frac{mg}{x}=\frac{(6.9)(9.8)}{0.29}=233.2 N/m[/tex]

2)

The oscillation frequency of a spring-mass system is given by

[tex]f=\frac{1}{2\pi}\sqrt{\frac{k}{m}}[/tex]

where

k is the spring constant

m is the mass

In this problem,

k = 233.2 N/m is the spring constant

m = 6.9 kg is the mass

Substituting, we find the frequency:

[tex]f=\frac{1}{2\pi}\sqrt{\frac{233.2}{6.9}}=0.93 Hz[/tex]

3)

The velocity of the block at time t is given by the equation:

[tex]v(t) = -v_0 cos(\omega t)[/tex]

where

[tex]v_0 = 4.1 m/s[/tex] is the initial speed

[tex]\omega[/tex] is the angular frequency

t is the time

The angular frequency can be found from the frequency:

[tex]\omega=2\pi f=2\pi(0.93)=5.84 rad/s[/tex]

And substituting t = 0.42 s, we find the velocity of the block at this time:

[tex]v(t)=-4.1 cos ((5.84)(0.42))=3.2 m/s[/tex]

4)

The maximum acceleration of the block is given by

[tex]a_{max} = \omega^2 A[/tex] (1)

where

[tex]\omega=5.84 rad/s[/tex] is the angular frequency

A is the amplitude

The amplitude is related to the initial velocity by the equation:

[tex]v_0=\omega A[/tex] (2)

Combining (1) and (2), we find

[tex]a_{max}=v_0 \omega[/tex]

And substituting [tex]v_0 = 4.1 m/s[/tex], we find

[tex]a_{max}=(4.1)(5.84)=23.9 m/s^2[/tex]

5)

The acceleration at time t can be found by calculating the derivative of v(t), and it is given by the equation

[tex]a(t) = a_{max} sin(\omega t)[/tex]

where

[tex]a_{max}=23.9 m/s^2[/tex] is the maximum acceleration

[tex]\omega=5.84 rad/s[/tex] is the angular frequency

t is the time

Substituting t = 0.42 s,

[tex]a(t)=(23.9)sin((5.84)(0.42))=15.2 m/s^2[/tex]

Finally, the net force on the block can be found by using Newton's second law:

[tex]F=ma=(6.9)(15.2)=104.9 N[/tex]

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