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 −2 inches per second. If Lisa holds her hand 5 feet above the lake's surface, how far from Lisa's hand is the rock 4 seconds after it hits the surface?

Answer 1

Answer:

• 5 ft 8 in or 68 in

Step-by-step explanation:

In 4 seconds the rock will be at:

• 2*4 = 8 in from the surface

Add 5 feet to this to get the required distance:

• 5 ft + 8 in = 5*12 in + 8 in = 68 in

Answer 2

Distance after 8s:-

$\\ \rm\longmapsto 4(-2)=-8in$

Now

Distance:-

$\\ \rm\longmapsto 5-(-8)$

$\\ \rm\longmapsto 5ft+8in$

• 1ft=12in

$\\ \rm\longmapsto 5ft+3/4ft$

$\\ \rm\longmapsto 23/4ft$

$\\ \rm\longmapsto 5.7ft$

• Convert to in

$\\ \rm\longmapsto 5.7\times 12$

$\\ \rm\longmapsto 68in$