Solution of Problem 43, Chapter 8, Fundamentals Of Physics 9th - Halliday & Resnick

 

Solution of Problem 43, Chapter 8

Fundamentals Of Physics 9th - Halliday & Resnick

Question:

A collie drags its bed box across a floor by applying a horizontal force of 8.0 N. The kinetic frictional force acting on the boc has magnitude 5.0 N. As the box is dragged through 0.70 m along the way, what are (a) the work done by the collie's applied force and (b) the increase in thermal energy of the bed and floor?

Answer:

a) Work done by Collie's applied force:

    Work  = Force * distance * cos𝚹

    Where 𝚹 = 0 (force is horizontal)

    Substituting the values:

    Work = 8.0 N * 0.70 m * cos (0°)

    Work =  5.6 J

b) Increase in thermal energy

    ΔQ = Work done by friction force = friction force * distance

    Substituting the values:

    ΔQ = 5.0 N * 0.70 m

    ΔQ =  3.5 J