0
$\begingroup$

Ive been given this question...

A child of mass 30kg holds on to a playground rope that is suspended at each end. On one side of the child, the rope is at an angle of 45◦ to the horizontal, and on the other side it is at an angle of 30◦ to the horizontal. Calculate the tension in each side of the rope, in newtons to two significant figures.

I've modeled it as shown below, but for some reason i keep getting a negative tension. I'm not sure where I've gone wrong.

Model

Attempt at F

Thanks for any help Mike

  • 0
    I forgot to point out i points horizontally right and j points vertically up – 2017-01-23

1 Answers 1

0

As with any force, the magnitude is always positive. Whether its positive or negative depends on its direction and what sign you've assigned to that direction.

So if you choose the typical choice, that "up" is positive, then the tension holding the ball from sinking is up, so its positive. And the tension keeping the ball from rising is down, so its negative.

  • 0
    But F shouldn't have a negative value should it? – 2017-01-23
  • 0
    Tension is nonnegative. But if -ve then that negative sign for direction. If you don't want to think according to direction you can find magnitude of its value. – 2017-01-23