Question

189. A man has to exert a force of 10 N at the edge of a door to push it open. How much
force will the man have to exert if he pushes the centre of the door?
(A)
(C)
10 N
15 N
(B) 5 N
(D) 20 N
ஒரு நபர் ஒரு கதவை அதன் முனையில் (கைப்பிடியில்) 10 N அளவு விசையை செலுத்தி
திறப்பார், எனில் அதே கதவை அதன் மையப் பகுதியில் இருந்து திறக்க தேவைப்படும் விசையின்
மதிப்பு என்ன?
(B) 5 N
(A)
(C)
10 N
15 N
(D)
20 N
90. The first battery was made by
(A)
Joule
(B) George Simon ohm​

Answer 1

Answer:

We need the 20 N force to open the door

Step-by-step explanation:

Let the width of door is L m then

We are given

F1 = 10 N

r = width of door = L m

By using formula of torque we can write

τ1 = r × F1 =

Putting values we get

τ1 = r × F1 =10L

⇒ τ1 = 10L

Now if the length is half then

τ2 = L/2 × F2 = F2(L/2)

And

If τ1 = τ2 then

    10L = F2(L/2)

Dividing by L on both sides we get

      10 = F / 2

⇒     F = 20 N

Thus we need the 20 N force to open the door

Answer 2

Given: force = 10N

To find: force to exert if he pushes the center of the door

Solution:

• To find force exerted we need to specify the width of the door,

• So let the width of door be x.

• Also we are given, that

            Force = 10 N

            r = width of door = x

• We have the formula for the torque,

              τ1 = F1 x r

• Putting both the values in formula, we get:

              τ1 = r × F1

              = 10x

• so, τ1 = 10x

• Now, consider,  if the length becomes half, we get:

              τ2 = x/2 × F2 = F2(x/2)

• Also if,

• If τ1 = τ2 then

                10x =  F2(x/2)

• Further calculating we get:

               10 = F / 2

                F = 20 N

Answer:

       Force to exert if he pushes the center of the door is 20 N