An object stays at rest until what happens to it?
a. inertia releases it.
b. gravity overcomes friction.
c. friction builds up and moves the object.
d. an outside or unbalanced force acts upon the object.

How is coal extracted from mountaintop removal mines? a. dynamite is used to create underground tunnels where miners go to extract the coal. b. dynamite is used to break apart rocks and then draglines are used to remove the broken rock and reach the coal. c. coal in mountaintops is extracted by digging strips in the landscape to reach the coal. d. placer deposits in mountain river bottoms are removed by