Question

Figure Qla shows a safety trap for trucks (not to scale) that has been installed on a very steep slope to prevent runaway trucks from crashing. It consists of a rough run- off lane of length 20m (beginning at point A) and a buffer designed to stop the vehicle. The buffer can be modelled as a spring of spring constant 750 kN/m and natural length 4m, compressed to 1m using cables. The run-off lane provides an effective coefficient of kinetic friction 0.4. The buffer and spring are considered to have negligible mass. Q1 (a) A truck of weight 400kN enters the run-off lane at point A with vA 5 m/s, then strikes the buffer and pushes it forward before stopping. Determine the length by which the buffer is pushed forward by stepping through the following questions. Draw the free-body diagram for the truck, showing all forces acting on it (i) 12] when it is contact with the buffer. Evaluate the work done by all forces acting on the truck. Using the principle of work and energy, calculate the length by which the (ii) (iii) 14] buffer is pushed forward when the truck comes to rest 13 5 12 k 750 kN/m 20m Figure Qla

Answer 1

13 g coso a = g (Simo-u (oso) = 8 (0.386. .Чх 0.323 ) t Coork done. bz frictiom orCe Velocity Chen truck YCaches to the S

emCmServai t Spring 400x(03-х box 31.2 750 x ผู้ 3.8 1.303 m x
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