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dusya [7]
3 years ago
7

A father racing his son has 1/3 the kinetic energy of the son, who has 1/4 the mass of the father. The father speeds up by 1.5 m

/s and then has the same kinetic energy as the son. What are the original speeds of
(a) the father and
(b) the son?
Physics
1 answer:
Feliz [49]3 years ago
8 0

Explanation:

Let the speeds of father and son are v_f\ and\ v_s. The kinetic energies of father and son are K_f\ and\ K_s. The mass of father and son are  m_f\ and\ m_s

(a) According to given conditions, K_f=\dfrac{1}{3}K_s

And m_s=\dfrac{1}{4}m_f

Kinetic energy of father is given by :

K_f=\dfrac{1}{2}m_fv_f^2.............(1)

Kinetic energy of son is given by :

K_s=\dfrac{1}{2}m_sv_s^2...........(2)

From equation (1), (2) we get :

\dfrac{v_f^2}{v_s^2}=\dfrac{1}{12}..............(3)

If the speed of father is speed up by 1.5 m/s, so the ratio of kinetic energies is given by :

\dfrac{K_f}{K_s}=\dfrac{1/2m_f(v_f+1.5)^2}{1/2m_sv_s^2}

v_s^2=4(v_f+1.5)^2

Using equation (3) in above equation, we get :

v_f=\dfrac{1.5}{\sqrt3-1}=2.04\ m/s

(b) Put the value of v_f in equation (3) as :

v_s=7.09\ m/s

Hence, this is the required solution.

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