Answer:
a = - 1.8 m / s²
Explanation:
To solve this exercise let's use Newton's second law, let's start by defining a reference system with the x axis parallel to the plane, in the adjoint we can see a diagram of the forces
let's break down the weight
sin 42 = Wₓ / W
cos 42 = W_y / W
Wₓ = W sin 42
W_y = W cos 42
Y axis
N- W_y = 0
N = W_y
N = mg cos 42
X axis
fr -Wₓ = m a
a = (fr - mg sin 42) / m
the friction force has the formula
fr = μ N
fr = μ mg cos 42
we substitute
a = (μ g cos 42– g sin 42)
a = g (μ cos 42 - sin 42)
let's calculate
a = 9.8 (0.650 cos 42 - sin 42)
a = - 1.8 m / s²
The negative sign indicates that the acceleration is downward, so the boy is descending.
