Problem 44 (Plug-n-chug). A frictionless horizontal air track has a horizontal spring at one end, with a spring constant of 800 N/m. A glider with a mass of 500 g

is pressed against the spring, compressing it by 4 cm. When the glider is released, the spring pushes it down the track. How fast is the glider moving when it leaves the spring? (a)20 cm/s (b) 40 сm/s (c) 80 cm/s (d) 160 cm/s (e) None of these