Question

# You have three coins that are identical in appearance. One is counterfeit, and its mass is different from the mass of the two legitimate coins. You also have an equal-arm balance (a device that compares the masses of two objects and “balances” if they are equal). Describe how you can determine which is the counterfeit coin and whether it is heavier or lighter than the legitimate coins by making only two measurements with the balance.

Solution

Verified
Step 1
1 of 4

We use the equal-arm balance to determine the mass difference between the coins, as shown in the figure below. When the coins are the same weight, the bar will be horizontal with the base on which the device stands. However, when some object is heavier, the bar will tilt. For example, in the figure below, a left coin is heavier than a right coin since it's closer to the ground.

## Recommended textbook solutions

#### Physics for Scientists and Engineers: A Strategic Approach with Modern Physics

4th EditionISBN: 9780133942651 (8 more)Randall D. Knight
3,508 solutions

#### Principles and Practice of Physics

1st EditionISBN: 9780321949202Eric Mazur
3,221 solutions

#### Mathematical Methods in the Physical Sciences

3rd EditionISBN: 9780471198260 (1 more)Mary L. Boas
3,355 solutions

#### Fundamentals of Physics

10th EditionISBN: 9781118230718David Halliday, Jearl Walker, Robert Resnick
8,950 solutions