A 8000 kg freight car rolls along rails with negligible friction. The car is bro

Question

A 8000 kg freight car rolls along rails with negligible friction. The car is brought to rest by a combination of two coiled springs as illustrated in the figure below. Both springs are described by Hooke's law with k1 = 1500 N/m and k2 = 3700 N/m. After the first spring compresses a distance of 25.0 cm, the second spring acts with the first to increase the force as additional compression occurs as shown in the graph. The car comes to rest 45.0 cm after first contacting the two-spring system. Find the car's initial speed.

Explanation / Answer

from the law of conservtion of linear momentum

KE of car = final PE of two springs

0.5 m v^2 = 0.5 k1 x2^2 + 0.5 * k2 * (x2-x1)^2

0.5 * 8000 * v^2 = 0.5 * 1500 * 0.45^2 + (0.5 * 3700 * ( 0.45 -0.25)^2

initial speed of car = V = 0.237 m/s

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