Question

Lisa is standing on a dock beside a lake. She drops a rock from her hand into the lake. After the rock hits the surface of the lake, the rock's distance from the lake's surface changes at a rate of −3 inches per second. If Lisa holds her hand 5 feet above the lake's surface, how far from Lisa's hand is the rock 5 seconds after it hits the surface?

Answer 1

After 5 seconds, the rock is 20 feet away from Lisa's hand.

Answer 2

If the rock is going down at 3 inches per second, then to find how far beneath the surface of the lake the rock was after 5 seconds, just multiply 3*5.

After 5 seconds, the rock is at -15 feet.

To find how far away from Lisa's hand the rock is, we need to add 5 because her hand is 5 feet above the lake's surface.

After 5 seconds, the rock is 20 feet away from Lisa's hand.