A rod of mass M = 116 g and length L = 49 cm can rotate about a hinge at its left end and is initially at rest. A putty ball of mass m = 14 g, moving with speed V= 6 m/s, strikes the rod at angle A = 37º a distance D=L/4 from the end and sticks to the rod after the collision.
(A) What is the total moment of inertia, 1, with respect to the hinge, of the rod-ball-system after the collision?
(B) Enter an expression for the angular speed w of the system immediately after the collision, in terms of m, V, D, 0,
(C) Calculate the rotational kinetic energy, in joules, of the system after the collision

Respuesta :

Answer:

a) Before:

I = 0.00928 kg*m^2

after:

I = 0.00949 kg*m^2

b) W = 65.25 rad/s

c) k = 20.2021 J

Explanation:

a)The moment of inertia before the collision is done by:

I = [tex]\frac{1}{3}ML^2[/tex]

where M is the mass and L is the length.

I = [tex]\frac{1}{3}(0.116 kg)(0.49 m)^2[/tex]

I = 0.00928 kg*m^2

After the collision the moment of inertia is:

I = [tex]\frac{1}{3}ML^2 + M_mR^2[/tex]

the first part is the moment of inertia before the collision but now we plus the mass of the putty ball ([tex]M_m[/tex] and the distance R where the putty ball strickes.

I = [tex]\frac{1}{3}(0.116)(0.49)^2 + (0.014)(0.49/4)^2[/tex]

I = 0.00949 kg*m^2

b)

For answer this we will use the law of the conservation of the angular momentum:

[tex]L_i = L_f[/tex]

Adittionally, the angular momentum L could be calculated by:

L = MDV

where M is the mass, V is the velocity and D is the lever arm, or:

L = IW

where I is the moment of inertia and W is the angular velocity.

Following the equations, now we have:

[tex]M_pV_pD = I_sW[/tex]

where [tex]M_p[/tex] is the mass of the putty ball, [tex]V_p[/tex] is the velocity of the putty ball, and [tex]I_s[/tex] is the moment of inertia after the collition

replacing the data:

[tex](0.014)(6)(12.25*sin(37)) = (0.00949 kg*m^2)W[/tex]

solving for W, we get:

W = 65.25 rad/s

c)

The kinetic energy is calculated by the next equation:

K = [tex]\frac{1}{2}I_sW^2[/tex]

replacing the data:

k = [tex]\frac{1}{2}(0.00949)(65.25)^2[/tex]

k = 20.2021 J