A 680-newton student runs up a flight of stairs 35 meters high in 11.4 seconds. The student takes 8 5 seconds to run up the same flight of stairs during a second trial

d

explanation:

v=uf/(u-f)

= 5.10/(5-10) convex lens has positive focal length

=50/-5

=-10 cm (formed at other side)

the answer is f1 and d2 because if you put equal force on those two points the beam would balance trust me on this

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