Question

If a force of 30N is applied to an object of mass 8kg which is kept on a surface, it achieves an acceleration of 3m/s. What is the frictional force in Newton between the object and the surface?
a) 0
b) 6
c) 24
d) 54
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Answer 1

By Newton's second law, the net force on the object acting parallel to the surface is

∑ F = F[applied] - F[friction] = (8k g) (3 m/s²)

If F[applied] = 30 N, then

30 N - F[friction] = 24 N   ⇒   F[friction] = 6 N

so the answer is B.