# Two children are balanced on a seesaw of negligible mass. The first child has a mass of 23 kg and...

## Question:

Two children are balanced on a seesaw of negligible mass. The first child has a mass of 23 kg and sits 0.61 m from the pivot. If the second child has a mass of 40 kg, how far is she, in m, from the pivot?

## Moment about pivot

When a force acts on the produces turning effect about fixed axis of rotation then it is called a moment. It is often called as torque. The moment is a product of force and distance between the line of action of force and pivot. In the case of the design of beams, the moment is calculated.

Moment = Force {eq}\times {/eq} distance to the pivot

As we increase the distance to the pivot then the moment will also increase.

## Answer and Explanation:

{eq}\textbf {Given data} {/eq}

Mass of first child is {eq}m_1 =23 \:kg {/eq}

The distance of the first child from pivot {eq}l_1=0 61 \:m {/eq}

Mass of second child {eq}m_2= 40\: kg {/eq}

The distance of the second child from the pivot is {eq}l_2 {/eq} When the seesaw is balanced then moment created by the first child about pivot is equal to the moment created by the second child about pivot.

{eq}m_1l_1=m_2l_2 {/eq}

{eq}l_2=\dfrac {m_1l_1} {m_2} {/eq}

{eq}l_2=\dfrac {23\times 0.61} {40} {/eq}

{eq}l_2=0.35\: m {/eq}

So second child is at {eq}0.35 \:m {/eq} from the pivot.

#### Learn more about this topic: Torque in Physics: Equation, Examples & Problems

from Physics: Middle School

Chapter 3 / Lesson 13
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