Spring Forces Question

Question

 A light spring with a force constant of 32 N/m is connected to a wall and to a 1.8-kg toy bulldozer. When the electric motor in the bulldozer is turned on, it stretches the spring for a distance of 45 cm before its tread begins to slip on the floor and it accelerates back towards the wall at a rate of 0.784 m/s2. What is the coefficient of dynamic friction between the treads and the floor?

Answer 1

 A light spring with a force constant of 32 N/m is connected to a wall and to a 1.8-kg toy bulldozer. When the electric motor in the bulldozer is turned on, it stretches the spring for a distance of 45 cm before its tread begins to slip on the floor and it accelerates back towards the wall at a rate of 0.784 m/s2. What is the coefficient of dynamic friction between the treads and the floor?

Extension = 0.45 m

Elastic force = Spring Constant * Extension= 32 *0.45 = 14.4 N

Force acting towards wall = Mass* acceleration = 1.8*0.784 = 1.4112

force of friction = 14.4 - 1.4112 = 12.98 N

Coefficient of dynamic Friction = Force of friction / ( Mass * g ) = 12.98/(1.8*9.8) = 0.74 ( No units )