Hi Gin! In this question, we need to use the equation that follows from Newton's laws:
sumF=m*a
In this case, the forces in the x-direction are the horizontal pulling force and the force of friction, and the forces in the y-direction are the normal force and the force of gravity.
So, completing this equation in the x-direction gives us the following:
sumFx = Fp - Ff = m*a (Fp is the force of the pull, and Ff is the force due to friction)
Ff can be found using the following equation: Ff = Fn * coeff of kinetic friction. We don't yet know Fn (the normal force), so we need to solve for it using the sumFy equation.
sumFy = Fn - Fg = m*a
Acceleration is 0, so the equation is the following:
sumFy = Fn - Fg = 0
Therefore, Fn = Fg = m * g = 2kg * 9.8m/s^2 = 19.6 N
Now that we have the Normal Force (Fn), we can plug that into our equation for the Ff from above:
Ff = Fn * coefficient of kinetic friction = 19.6 N * 0.12 = 2.35 N
Now that we have the Ff, we can plug that into our equation for sumFx from above:
sumFx = Fp - Ff = m * a
4N - 2.35N = 2kg * a
Solving for a, we get 0.825 m/s^2.
Hopefully this helps! Let me know if you have any questions!!
Justin
