Answer:
F = 52.93 [N]
Explanation:
Since the Rock is thrown upwards, there are only two forces, one is the force of the rubber (55[N]) and the other is the force of gravitational acceleration acting in the opposite direction to the movement of the rock, therefore this acceleration will be taken as negative.
F = 55 - m*g
where:
F = total force [N] (units of Newtons)
m = mass = 0.21 [kg]
g = gravity acceleration = 9.81 [m/s²]
F = 55 - (0.21*9.81)
F = 52.93 [N]
