Whenever an object is thrown vertically upwards or it movesvertically downwards, the gravitational pull of Earth gives uniformacceleration a=+g=10 m s–2 in the vertically downward direction. Ifm = mass of the object, then net force on it = mg
Here m = 0.05 kg = mass of the pebble.
(a) ∴ Net force on the pebble = mg
(∵ a = g)
= 0.05 × 10 = 0.5 N
(acts vertically downwards)
(b) Net force on the pebble = mg
(∵ a = g)
= 0.05 × 10 = 0.5 N
(acts vertically downwards)
(c) When the stone is at the highest point then also the net force (= mg)acts in vertically downward direction
∴ Net force on the pebble = mg = 0.05 × 10 = 0.5 N
If the pebble was thrown at an angle of 45° with the horizontal direction,then it will have horizontal and vertical components of velocity which willnot affect the force on the pebble. Hence our answer will not change inany cases. However in case (c), the pebble will not be at rest at the highestpoint. It will have a horizontal component of velocity at this point.