Suppose a 350-g kookaburra (a large kingfisher bird) picks up a 75-g snake and raises it 2.5 m from the ground to a branch. (a) how much work did the bird do on the snake? (b) how much work did it do to raise its own center of mass to the branch?

(a) The work done by the bird to raise the snake on the branch is equal to the product between the weight of the snake and the height of the branch above the ground:

where is the mass of the snake and is the height of the branch with respect to the ground. Substituting numbers into the equation, we find

(b) The work the bird did to raise its own centre of mass from the ground to the branch is equal to the product between the bird's weight and the height of the branch:

where is the mass of the bird. Substituting numbers into the equation, we find

causes

fossil fuels burn

cities become more industrialized

human population grows worldwide