Answer:
B. 7 m/s²
Explanation:
Draw a free body diagram of the box. There are three forces:
Normal force N pushing up.
Weight force mg pulling down.
Friction force Nμ pushing against the direction of motion.
Sum of forces in the y direction:
∑F = ma
N − mg = 0
N = mg
Sum of forces in the x direction:
∑F = ma
-Nμ = ma
-mgμ = ma
a = -gμ
a = -(9.8 m/s²) (0.7)
a ≈ -7 m/s²
The magnitude of the box's acceleration is 7 m/s².
