13. 2 points I Previcus Answers HRW10 7.P.005. My Notes Ask Your Teacher A fathe

Question

13. 2 points I Previcus Answers HRW10 7.P.005. My Notes Ask Your Teacher A father racing his son has half the kinetic energy of the son, who has one-third the mass of the father. The father speeds up by 2.7 m/s and then has the same kinetic energy as the son. (a) What is the original speed of the father? 3.7 m/s (b) What is the original speed of the son? 11.1 X myfs Did you set up an algebralc statement of the first sentence? Instead of using the symbol K, use the definition 0.5mv2. Did you write a similar equation for the second sentence?

Explanation / Answer

mass of the father as m and his initial speed vi. The initial kinetic energy o f the father is

Ki = 1/2*Kson

Vf = Vi + 2.7 m/s

a)

Ki = 1/2Kf

1/2mvi^2 = 1/2(1/2m(vi + 2.7)^2)

1/2 and m are cancled

vi^2 = 1/2(vi^2 + 5.4vi + 7.29)

vi^2 = 1/2vi^2 + 2.7vi + 3.645

0.5vi^2 - 2.7vi - 3.645 = 0

solve quadratic equation

positive root is 6.52

vi = 6.52 m/s

b)

Ki = 1/2*Kson

1/2mvi^2 = 1/2[(1/2)m/3)Vson^2

vi^2 = (1/6)Vson^2

6 x vi^2 = Vson^2

Vson = sqrt(6 x vi^2)

Vson = 2.449*vi

Vson = 2.449 x 6.52 m/s

Vson = 15.971 m/s

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