Question

Which of the following are examples of work being done on an object? Choose all 4 that apply.(1 point)
Responses

holding a 45 kg barbell over your head
holding a 45 kg barbell over your head

lifting a bag of groceries
lifting a bag of groceries

pushing on a car that will not move
pushing on a car that will not move

carrying a box up a flight of stairs
carrying a box up a flight of stairs

lifting a rock off the ground
lifting a rock off the ground

wind blowing against a tree
wind blowing against a tree

carrying a bag of groceries through the store.
carrying a bag of groceries through the store.

pushing a grocery cart through the store

Answer 1

Correct choices (4):
- lifting a bag of groceries — yes (force upward, object displaced upward)
- carrying a box up a flight of stairs — yes (force against gravity while box is displaced upward)
- lifting a rock off the ground — yes (force and displacement in same direction)
- pushing a grocery cart through the store — yes (force has a displacement component along the push)

Not work (briefly why):
- holding a 45 kg barbell over your head — no displacement, so no mechanical work on the barbell
- pushing on a car that will not move — no displacement → no work
- wind blowing against a tree — no significant displacement of the tree (as stated), so no work
- carrying a bag of groceries through the store — vertical support force with horizontal displacement has zero force–displacement dot product, so no mechanical work on the bag