- #1
Saitama
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Homework Statement
Question 1)
In the figure below, k=100 N/m, M=1 kg and F=10N. A sharp blow by some external agent imparts the speed of 2 m/s to the block towards left. Find the amplitude of the resulting simple harmonic motion.
Question 2)
The string and the spring shown in the figure below are light . The pulley has a moment of Inertia I about its CoM axis and the string does not slip over it. Find the time period of mass m.
Homework Equations
The Attempt at a Solution
For the first Question 1, i used the energy conservation to solve the problem.
Firstly, i found the initial compression in the spring and then formulated the equation as:-
[tex]\frac{1}{2}Mv^2+\frac{1}{2}kx_o^2=Fx+\frac{1}{2}k(x+x_o)^2[/tex]
xo=Initial compression in the spring
v=velocity imparted to the block
x=Distance which the block covers after the velocity is imparted (This will be the amplitude)
Now when i plug in the values, i don't get the answer stated in answer key. I don't understand where i am going wrong.
For Question 2), my teacher helped me to formulate the equation.
We take mass m down by a distance of x and then formulate the equation for total energy.
[tex]E=-mgx+\frac{1}{2}k(x+x_0)^2+\frac{1}{2}mv^2+\frac{1}{2}I(\frac{v}{r})^2[/tex]
In SHM, dE/dt=0 but that's the next step, i have a problem in the equation above.
Why we use a negative sign before mgx? The displacement x and the force mg are in the same direction so why the negative sign appears?