X-Post: Can someone verify the Net Force

[Blossom'sGirl]

I know this is not really high school level, but I thought I may get a response here.

 

This is on p. 105 of the CPO Middle School Physical science book

 

A box has a force of 60N up and 80N to the east. What is the net force?

 

I get 10N at a 45 degree angle in a north east direction. The book gets 11.8N at a 45 degree angle.

 

I haven't done these in years but I thought it was a simple a squared + b squared = c squared.

[regentrude]

A box has a force of 60N up and 80N to the east. What is the net force?

 

I get 10N at a 45 degree angle in a north east direction. The book gets 11.8N at a 45 degree angle.

 

I haven't done these in years but I thought it was a simple a squared + b squared = c squared.

 

The forces are directed at right angles, so the net force can be found from the Pythagorean theorem:

Fnet= sqrt( F_up^2+F_east^2)= 100N. (This is a 3-4-5 triangle.)

 

The direction of the net force requires trigonometry. tan theta= 80/60, so theta=53.1 degrees east of up. Calculating this is beyond the scope of your course.

The angle can NOT be 45 degrees, because that would require the forces to be equal.

 

Are there any other forces? Weight? Because otherwise, how can they come up with the answers in the book?