Question

Mark pushes his broken car 150 m down the block to his friend's house. He has to exert a 160 N horizontal force to push the car at a constant speed. How much thermal energy is created in the tires and road during this short trip?

Answer 1

the energy dissipated as heat

E dissipated = 24 kJ

Step-by-step explanation:

From Newton's second law:

F= m*a

since the car moves at constant speed a=0 , then

F = 0

F1 - Fr = 0 , where Fr = friction force, F1= horizontal force

Fr=F1

the energy dissipated as heat is equal to the work done by Mark, therefore

E dissipated = W = ∫ F dx = Fr ∫ dx = Fr*L , L= distance to Mark's friend house

then

E dissipated = Fr*L = 160 N * 150 m = 24000 J = 24 kJ