Inelastic Collision.

(e) How important are the neglected external forces during the collision?Suppose the car applied its brakes so that it slidesjust before the collision. The coefficient of kineticfriction is 0.300.NN = mg = 7.84×10fk= μ N = 2.35×10k3( N )3( N )f kmgComparison of these forces with the average force exerted on the car (expressed as a %)Force (N) %By truckf k3.20x10 52.35x10 3 0.73(f) After the collision, how the truck slides a distance of 20.0 (m) beforehitting a guard rail that acts like a spring. The maximum compression ofthe spring is 1.50 (m). Find “k” of the guardrail.v i = 13 m/s21.5 mx i = 0We use the Energy Method to find “k” the forceconstant. The coefficient of kinetic friction is0.300.x f= 1.5 mN = mg = 3.92x10 4 (N)f k= μ kN = 1.18x10 4 (N).The pseudo work done by the kinetic friction force between the position of thetruck just after the collision and when it is at rest momentarily with the guardrail at its maximum compression is:W= f( cos 180) 21.5 = −2.54×10 ( J )5f k k3

We Apply the Work Energy Method to the truck between “I” and “f”:KΔ + Δs=⎛ 1 2 ⎞⎜0− mvi⎝2mvk =U2i+ 2Wx2fW⎟ +⎠fkfk⎛ 1⎜ kx⎝ 22f⎞− 0⎟= W⎠= 7.47×104fk(Nm)4