Question

The force the attraction between two magnets is F Newtons. This force is inversely

proportional to the square of the distance, d centimetres, between the magnets.
(a) When the magnets are a certain distance apart, the force is 10 Newtons.
What is the force when the distance is doubled ?
(b) (i) Write down a formula connecting F,d and a constant k.
(ii) When the magnets are 3 cm apart, the force is 2 Newtons.
Find the force when they are 5 cm apart.

Answer 1

1a

f is inversely proportional to d² so when d is d f=10N and when d is doubled F is 5/2N

1bi K=Fd²

1bii

since K=fd² when d is 3cm and F is 2N k=18

then when d=5

F is 18/25N