Option D) A drop of mercury is both a pure substance and and element.
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Explanation:
Work done is given by the product of force and displacement.
Case 1,
1. A boy lifts a 2-newton box 0.8 meters.
W = 2 N × 0.8 m = 1.6 J
2. A boy lifts a 5-newton box 0.8 meters.
W = 5 N × 0.8 m = 4 J
3. A boy lifts a 8-newton box 0.2 meters.
W = 8 N × 0.2 m = 1.6 J
4. A boy lifts a 10-newton box 0.2 meters.
W = 10 N × 0.2 m = 2 J
Out of the four options, in option (2) ''A boy lifts a 5-newton box 0.8 meters'', the work done is 4 J. Hence, the greatest work done is 4 J.
Hello!
Let's begin by doing a summation of torques, placing the pivot point at the attachment point of the rod to the wall.

We have two torques acting on the rod:
- Force of gravity at the center of mass (d = 0.700 m)
- VERTICAL component of the tension at a distance of 'L' (L = 2.200 m)
Both of these act in opposite directions. Let's use the equation for torque:

Doing the summation using their respective lever arms:


Our unknown is 'theta' - the angle the string forms with the rod. Let's use right triangle trig to solve:

Now, let's solve for 'T'.

Plugging in the values:

Conductors have many free electrons
insulators have few free electrons
conductors are ideal for electrical wiring