What has changed when a gardener uses a lever to lift a rock, instead of lifting it by hand? a. more force is applied over a shorter distance. b. more force is applied over a longer distance. c. less force is applied over a longer distance. d. less force is applied over a shorter distance.

D. Less force is applied over a longer distance.

Explanation:

A lever converts a small force at one end to larger force at the other end. When gardener was lifting the rock by his hand, he had exert larger force at a short distance. The same force required to lift the rock can be exerted if a small force is applied at a larger distance. This is done by the lever used by the gardener. By using lever, the gardener is getting mechanical advantage. Mechanical advantage is the ratio of output force and input force.  

Option (D)

Explanation:

A lever is usually defined as a hard rod that turns about an axis (fulcrum), which is mainly used to lift or move a heavy object by applying less amount of force. It makes the task easy. Since it works mechanically, so it can be considered as a mechanical advantage.

In the given condition, the gardener lifts a rock with the help of a lever, which signifies that less amount of force is applied over a relatively shorter distance.

Thus, the correct answer is option (D).

carbon traps heat so more of it makes it hotter causing global warming. during the ice age carbon levels in the atmosphere were low so it got very cold. so the common things between them is carbon levels in the atmosphere.