Question

multi - select: select all situations where work is done. a a teacher leans against a wall and becomes tired b an apple falls from a tree and hits isaac newton on his head c a box is pushed across a floor at constant speed d a box is pushed across a floor with an acceleration

Explanation:

Step1: Recall work - done formula

Work \(W = F\times d\times\cos\theta\), where \(F\) is force, \(d\) is displacement, and \(\theta\) is the angle between force and displacement. For work to be done, there must be a non - zero displacement in the direction of the force component.

Step2: Analyze option A

The teacher leaning against the wall has no displacement in the direction of the force exerted on the wall. So, \(d = 0\), and \(W=0\).

Step3: Analyze option B

The force of gravity acts on the apple, and it has a displacement in the direction of the gravitational force. So, work is done by gravity on the apple.

Step4: Analyze option C

A force is applied to push the box across the floor, and the box has a displacement in the direction of the applied force. So, work is done.

Step5: Analyze option D

A force is applied to accelerate the box across the floor, and the box has a displacement in the direction of the applied force. So, work is done.

Answer:

B. An apple falls from a tree and hits Isaac Newton on his head, C. A box is pushed across a floor at constant speed, D. A box is pushed across a floor with an acceleration