ICSE Class 9 Physics Question 12 of 20

Laws of Motion — Question 1

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Question 1

The force of attraction between two bodies at a certain separation is 10 N. What will be the force of attraction between them if the separation is reduced to half ?

Answer

As we know,

F=GMmR2\text{F} = \text{G}\dfrac{\text{M}\text{m}}{\text{R}^2}

Given,

F = 10 N, when separation = R,

Hence,

F1 = G M mR2\dfrac{\text {G M m}}{\text R^2} = 10 N     [Equation 1]

If separation = R2\dfrac{\text R}{2} then,

Substituting the values in the formula above, we get,

F2=G M m(R2)2F2=4G M mR2\text F_2 = \dfrac{\text {G M m}}{\big(\dfrac{\text R}{2}\big)^2} \\[0.5em] \text F_2 = \dfrac{4 \text {G M m}}{\text R^2} \\[0.5em]

F2=4×(G M mR2)\text F_2 = 4 \times \big(\dfrac{\text {G M m}}{\text R^2}\big)    [Equation 2]

Substituting the value of equation 1 in equation 2 we get,

F2 = 4 x 10 N = 40 N