Physics question...?

Question

A 1000 kg car rolling on a horizontal surface has speed v = 45 km/h when it strikes a horizontal coiled spring and is brought to rest in a distance of 2.2 m. What is the spring stiffness constant of the spring?

Answer 1

1/2mv^2=1/2kx^2
45 km/hr=45 km/hr*1/3600 hr/sec*1000 m/km=12.5 m/s

k=mv^2/x^2=1000*(12.5)^2/(2.2)^2=32.3

Answer 2

Convert v = 45 km/h = 12.5 m/s

Assuming no friction, we have

Ef = Ei

½ m vf² + ½ k xf² = ½ m vi² + ½ k xi

0 + ½ * k * 2.2² = ½ * 1000 * 12.5² + 0

k = 32283.1 N/m or 3 * 10^4 N/m