Answer:
d. 1000 N.
Explanation:
For the seesaw to be in equilibrium the moment on left of the fulcrum and the moment to the right of the fulcrum must be equal.
Let L be the distance on either side of fulcrum at which the boulder is kept
F be the minimum force used to pushdown the left end
According to principle
L×1000= L×F
F= 1000 N
Hence option D is correct