When Miller is positioning the can of explosive, he is clearly lifting a very heavy object. But the whole scene is set in zero gravity (or less, considering Eros is spinning). He and Diogo are using magnetic boots and tethers to avoid flying away. The bomb should be "weightless".
Objects in zero gravity still have a mass and moving them requires the overcoming of inertia (the tendency of a stationery object to remain stationery), even in zero g inertia is proportional to mass and a heavy object still requires greater force to move.
Objects in zero gravity still have a mass and moving them requires the overcoming of inertia (the tendency of a stationery object to remain stationery), even in zero g inertia is proportional to mass and a heavy object still requires greater force to move.
After the Nauvoo has been brought on course for Eros, Fred Johnson's tug drones disengage and return. But in a space collision between objects of irregular shape and consistency, however well planned, there will always be unpredictable variables. Thus there was always a chance that the deorbiting of Eros might not go as planned, put the asteroid on a collision course with something Fred would not want destroyed or make it miss the sun. The tug drones would be an option to correct that, so he should have taken them along.