Answer:
C. 7 m/s²
Step-by-step explanation:
The horizontal forces acting on the block are the 80 N tension, the 60 N tension, and friction. Apply Newton's second law:
∑F = ma
80 N − 60 N − F = (10 kg) (1 m/s²)
20 N − F = 10 N
F = 10 N
If S₁ goes away, the acceleration becomes:
∑F = ma
80 N − 10 N = (10 kg) a
70 N = (10 kg) a
a = 7 m/s²