Your favourite physics teacher lives in a high rise. A long light ideal vertical spring fastened much higher on the building suspends a light platform outside her balcony. Each morning she steps onto it and after a thrilling vertical descent her 50 kg body comes momentarily to rest just at ground level, 100 m below. A hook holds the spring stretched until it is time for her to release it and make the return trip to her balcony. One night she forgot she was carrying 20 kg of assignments to grade when she released the hook. How far was the platform below her balcony when she rst came to rest on this trip up? (SIN '94)