Weegy: If the truck is moving at constant velocity, the rock is moving also. So when it is dropped, it will simply land below where it was suspended. (More)

I'm making two assumptions, the astronaut is in zero gravity and the anvil is not fixed to anything but is floating like he is. The reaction will be opposite but equal in terms of energy. F=MA so the force that the astronaut and anvil are pushing against each other are the same but the masses are different. What will happen is that the astronaut will separate more quickly from the initial position than the anvil will. To calculate a number F1 and F2 are equal but opposite (opposite sign). The astronaut has a mass that is75/200 of the anvil which is .375 as a ratio.
You can see this if you set up the equation as
m1a1=m2a2,75a1=200a2,
a1 = 200/75 a2,
a1 = 2.67 a2.
Therefore, the acceleration of the astronaut is 2.67 times that of the anvil