Question

It is easier to pull a lawn roller then to push it because pulling:
A. Involves sliding friction
B. Involves rolling friction
C. Increases the effective weight
D. Decreases the normal reaction

Answer 1

We know that a push or pull needs us to expel energy , or we must do work and exert force. Here, we need to compare the force acting on the lawn roller when it is pushed or pulled, while comparing between pushing an object or pulling on object, we must consider the net force acting on the object

Complete answer:
Let us consider the following figure as shown below, and let the mass of the lawn roller be $m$.

When pushing with say some force $F$ at some angle to the ground. Then we can consider the parallel and the perpendicular components of force as shown in the figure.
Let us take into account the force due to gravity, in the downward direction as $m\;g$ and the normal $N$ in the upward direction, as shown in the figure.
Clearly, except the parallel component of force, others must cancel out each other, then we can say that
$N=mg+F_{per}$
Similarly, When pulling with say some force $F$ at some angle to the ground. Then we can consider the parallel and the perpendicular components of force as shown in the figure.

Let us take into account the force due to gravity, in the downward direction as $m\;g$ and the normal $N$ in the upward direction, as shown in the figure.
Clearly, except the parallel component of force, others must cancel out each other, then we can say that
$N=mg-F_{per}$
Comparing the normal $N$ during pushing and pulling, we see that the $N$ in pulling is lesser than that of pushing, hence, we can conclude that it is easier to pull than push.
Thus the correct answer is option D. decreases the normal reaction

Note:
Here, though we are exerting the force at some angle, the lawn roller must move in the x-direction or along the parallel component, hence we take the parallel component as the force needed to move the lawn. Thus the other forces acting on the lawn must be zero.