Explanation:
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Answer:
second one
e
i took it myself and got it right
PE = 1/2 kx²
mgh = 1/2 kx²
80.9.8.20 = 1/2 k.4²
k = 1960
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.
