Ashes from a campfire deep in a cave show carbon 14 activity of only one-eight the activity of fresh wood. How long ago was the campfire made ?

no. dot product   =0 when vecs at right angles

if the person is shown to have +90n, then ans is -10n.

if the person is shown to have -90n, then ans is +10n.

weight of the box is given as

here this is placed on the inclined of angle 42 degree

now this weight will have two components one is along the incline other is perpendicular to it

so here we need to apply a force parallel to incline opposite to its component of weight

so here the component of weight is given as

here we have

so it requires 75 n force to move it upwards