Question

010 (part 1 of 2) 10.0 points A crate is lifted vertically 1.5 m and then held at rest. The crate has weight 100 N (i.e., it is supported by an upward force of 100 N). How much work was done in lifting the crate from the ground to its final position? 1. No work was done. 2. None of these 3. More than 150 J 4. A bit less than 150 J 5. 150 J 011 (part 2 of 2) 10.0 points Now suppose the crate is lifted so rapidly that air resistance was significant during the raising. How much work was done by the lifting force as the box was raised 1.5 m? 1. Still 150 J 2. No work was done. 3. None of these 4. More than 150 J 5. A bit less than 150 J because the air partially supported the crate.

Answer 1

Part 1: The work done is, W = Fupwardd = (100 N)(1.5 m) = 150 J Here, Fupward is upward force. Part 2: The upward force acting is 100 N and weight of the crate is 100 N. Since, the air resistance was significant during raising the crate. So, the upward force is balanced by the gravity force and air resistance. This implies that the force will be greater than 100 N. The work done is equal to the product of force and displacement. Thus, the work done to raise the box must be greater than 150 J.