The total frictional force equals 60 N
Explanation:
We know that F - f = ma where F is the applied force, f is the frictional force, m the mass of the object and a its acceleration.
Now, since the cart moves with constant velocity, its acceleration is zero. So, a = 0.
So F - f = ma
F - f = m(0) = 0
F - f = 0
So, F = f
From the above, we see that the frictional force equals the applied force which is equal to 60 N.
So, f the total frictional force equals 60 N