Question

A seesaw made of a plank of mass 10.0 kg and length 3.00 m is balanced on a fulcrum 1.00 m from one end of the plank. A 20.0-kg mass rests on the end of the plank nearest the fulcrum. What mass must be on the other end if the plank remains balanced?

Answer 1

Answer:

The mass at the other end is 7.5 kg.

Explanation:

Let the mass is m.

Take the moments about the fulcrum.

20 x 1 = 10 x 0.5 + m x 2

20 = 5 + 2 m

2 m = 15

m = 7.5 kg

Answer 2

Answer:

7.5 kg

Explanation:

We are given that

$m_1=10 kg$

Length of plank, l=3 m

Distance of fulcrum from one end of the plank=1 m

$m_2=20 kg$

We have to find the mass must be on the other end if the plank remains balanced.

Let m be the mass must be on the other end if the plank remains balanced.

In balance condition

$20\times 1=10\times (1.5-1)+m\times (1.5+0.5)$

$20=10(0.5)+2m$

$20=5+2m$

$2m=20-5=15$

$\implies m=\frac{15}{2}$

$m=7.5 kg$

Hence, mass 7.5 kg   must be on the other end if the plank remains balanced.