a roller whose diameter is 20 in weight 72 lbs. what horizontal force is necessary to pull the roller
That will depend upon frictional torque on the roller axis. You have not provided enough information.
Is your word "weight" supposed to be the verb "weighs"? Does "in" mean inches?
I suspect you have omitted part of the question. Is the roller being pulled over a small bump, as in this question:
http://www.jiskha.com/display.cgi?id=1315698220 ? Such problems can be solved by balancing torques about the line of contact.
To calculate the horizontal force required to pull the roller, we need to consider the weight of the roller and the friction between the roller and the surface it's on.
First, let's clarify a couple of things. The weight of the roller is given as 72 lbs, which represents the force of gravity acting on it. We'll assume this force acts vertically downward.
Next, we need to account for the friction between the roller and the surface it's on. This friction opposes the motion of the roller and requires a horizontal force to overcome it. The frictional force depends on the coefficient of friction (μ) between the roller and the surface it's on, as well as the normal force (N) exerted by the roller on the surface.
Assuming the roller is on a level surface, the normal force is equal to the weight of the roller (N = 72 lbs).
Now, the frictional force (F_friction) can be calculated using the equation:
F_friction = μ * N
Here, we need to know the coefficient of friction (μ) between the roller and the surface it's on. This value can vary depending on the materials involved, such as rubber on concrete, metal on metal, etc. Without this information, we can't provide an exact value.
Once you have the coefficient of friction, you can substitute it into the equation along with the weight of the roller to calculate the frictional force. The horizontal force necessary to pull the roller will be equal to the frictional force.
So, to get the exact horizontal force necessary to pull the roller, you need to know the coefficient of friction between the roller and the surface it's on. With that information, you can use the equation F_friction = μ * N to determine the force required.