Final answer:
To balance a single penny placed 8 cm away from a pivot, two pennies must be placed 4 cm away each, and three pennies about 2.67 cm away on the opposite side to achieve the same torque.
Step-by-step explanation:
The penny experiment described in the question is related to the principles of torque and balance in physics. If you place a penny 8 cm away from the pivot, it creates a certain amount of torque due to gravity pulling down on it. To balance it with two pennies, they should be placed at a distance where the combined torque of the two pennies is equal to the torque of the single penny. This means placing two pennies each 4 cm away from the pivot on the opposite side (since 2 x 4 cm = 8 cm, and two pennies are twice the weight of one). For three pennies, they would need to be placed closer to the pivot, at a distance that makes the overall torque the same. Assuming the three pennies have the same mass as one another, they can be placed approximately 2.67 cm from the pivot (since 3 x 2.67 cm is approximately equal to 8 cm).