Which of the following is not an example of a force acting against inertia?
a. a thrown rock being pulled to the ground via gravity
b. a piece of cork floating up from deep underwater
c. a saucer balancing on a narrow precipice
d. a boulder rolling down a cliff

inertia is the force that compels something to keep the state its in. if it’s in motion inertia wants it to stay in motion and if it’s at rest then inertia wants it to stay at rest. i can think of gravity acting against, friction, etc examples so which one is right? my guess is c.

option B.  A piece of cork floating up from deep underwater.

Explanation:

Inertia is the property of a body to remain in it's original uniform motion unless been acted upon by an external force. It is the objects ability to resist change in motion. That is, its ability to resist acceleration.

The bold word 'Acceleration' says a lot about one most useful property of Inertia,and it's ability to resist acceleration couple with friction.

In option A the thrown rock is been decelerated from a hit .In this case there is no resistance to gravity.In option B which i believe is correct  . The piece of cork been submerged in a deep underwater is experiencing Acceleration.There is an ability of inertia to resist acceleration in this scenarioIn option C the is static without having experiencing an initial acceleration.And the ability to resist acceleration rule can't be applied to such case.In option D the boulder rolling down a cliff is similar to option A .There is no resistance to gravity as deceleration is been experienced.

The objects are acted upon by only one force. gravity. mass times the acceleration of gravity (-9.81meters/second squared).