Question

in which scenario is an animal doing work? check all that apply. a cat lifts up her kitten by its neck. a dog rubs his back against a large tree. a bird flies a worm from the ground to its nest in a tree. a goat butts its head against the barn wall. a horse pulls a wagon along a road.

Explanation:

Step1: Define work in physics

Work is done when a force causes an object to move in the direction of the force, $W = F\times d\times\cos\theta$ (where $W$ is work, $F$ is force, $d$ is displacement and $\theta$ is the angle between force and displacement). When $\theta = 0^{\circ}$, $\cos\theta=1$ and work is maximized.

Step2: Analyze cat - kitten scenario

The cat applies an upward force on the kitten and moves it upward. Force and displacement are in the same direction, so work is done.

Step3: Analyze dog - tree scenario

The dog pushes against the tree but the tree doesn't move. Since there is no displacement ($d = 0$), no work is done according to $W=F\times d\times\cos\theta$.

Step4: Analyze bird - worm scenario

The bird exerts a force to lift the worm and moves it from the ground to the nest. There is a displacement in the direction of the force, so work is done.

Step5: Analyze goat - barn wall scenario

The goat butts its head against the barn wall. The wall doesn't move, so with $d = 0$, no work is done.

Step6: Analyze horse - wagon scenario

The horse applies a force to pull the wagon and the wagon moves along the road. Force and displacement are in the same direction, so work is done.

Answer:

• A cat lifts up her kitten by its neck.
• A bird flies a worm from the ground to its nest in a tree.
• A horse pulls a wagon along a road.