Applying Newton's 2nd Law: A Scientist's Guide

[George2020]

Homework Statement

A. A tractor pulls a 150 kg rock to the right with a force of 1200 N against a force of friction of 750 N [left].
• Calculate the force of gravity on the rock and the normal force of the ground on the rock.
• Draw a FBD of the rock, and determine the magnitude and direction of the net force acting on the rock.
• Use Newton’s second law to find the acceleration of the rock

Relevant Equations

Force(net)=mass x acceleration

Hi ,
How to approach the problem?
Thanks

 

[Delta2]

Hi, and welcome to PF

According to the rules of PF, you should show some effort of your own before we are allowed to help you. The problem gives you almost step by step instructions on what to do. What is it that you don't understand?

• To calculate the normal force of the ground you ll have to apply Netwon's 2nd law in the y-axis (vertical direction) after you have found all the forces in this axis.
• To calculate the magnitude and direction of the net force acting on the rock you have to draw an FBD where you draw all forces in the x-axis (horizontal direction) and all the forces in the y-axis, and then taking the sum of the forces in each axis separately. Then use pythagorean theorem if needed to combine the net force in the y-axis with the net force in the x-axis to find the total net force.
• The problem implies there is motion only in the x-axis ("puls a 150kg rock to the right") so use that to your advantage. This effectively means that the acceleration along the y-axis is zero, while the acceleration along the x-axis $a_x$ might not be zero. Use Netwon's 2nd law $\sum F_x=ma_x$ in the x-axis to find the $a_x$.

 

[George2020]

Thanks for input. Is this the correct approach.

Force of gravity = 150 x 9.8= 1470N[d]
Force Normal = -1470N

Force Net = Force applied +Force Friction
= 1200N +(-750N)
=450N

Force net=ma
a=Force net/mass
= 450N/150kg
= 3m/s sq.

 

[Delta2]

Yes i think you are correct.