Question

f ∝ 1/d², when d = 5, f = 18. Hence,
(i) if d = 10 find f.
(ii) when f = 50 find d .

Answer 1

In order to remove the proportionality constant we have to bring a constant.

F ∝ 1/d², when d = 5, f = 18.

Let the constant be K.

F = K/d² or, K = F x d² = 18 x 25 = 450.

Now, when d = 10; F = 450/10 = 45.

if, F = 50;

So, we can write it as 50 = K/d²

or, 50 = 450/d²

or, d² = 450/50 = 9

or, d = squareroot of 9 = 3(Ans)

Answer 2

Hi ,

It is given that ,

f is inversely variance with d²

Therefore ,

f = C/d² [ C is a constant ]

f1 × d1² = f2 × d2²


i ) Here ,

d1 = 5 , f1 = 18

d2 = 10 , f2 = ?

f1 × d1² = f2 × d2²

18 × 5² = f2 × 10²

f2 = ( 18 × 25 )/100

f2 = 450/100

f2 = 4.5

ii ) d1 = 5 , f1 = 18 ,

f2 = 50 , d2 = ?

50 × d2² = 18 × 5²

d2² = ( 18 × 25 )/50

d2² = 9

d2 = √9

d2 = 3

I hope this helps you.

: )