# How to know what method to use when finding resultant forces?

I am quite confused as to what method should be used when finding resultant forces. Here are two examples of a question that asks to find the resultant force.

One requires the parallelogram law to be used.

The other requires finding the total in Fx and Fy.

So how do I identify which method I am supposed to use if its not stated during an exam? The questions seem very similar to each other. Is there specific details that I should bear in mind when it comes to the parallelogram law? Thank you in advance and sorry if this is a bit messy. It's my first time using this website.

• What is the difference between "parallelogram law" and "finding the total in Fx and Fy"? How would you do one or another? – VictorSeven Oct 15 '17 at 7:45
• The two methods give identical answers. (That's rather the whole point) If it's not stated during an exam, you can use either method. – Chris Oct 15 '17 at 8:10
• I agree with Chris. Note that on an exam, you should use whichever method is faster, because the exam is being timed. – David White Sep 4 '18 at 1:22

Two persons on different sides of a river, pull a boat towards themselves by means of a string. The boat moves forward in a straight line. The forces make $\theta$ and $\phi$ with the direction of motion of the boat. Find the resultant force on the boat.