At the steady state, a rotor spinning at the same speed will have the same absolute torque driving it, just balancing out losses from friction. the speed with which the motor/engine can change its output given a change in load that's the determining factor. Note that of course, it's the difference in torque characteristics, i.e. I'd be very surprised if the rotor had time to lose enough angular momentum that the difference in torque curves between the electric motor and an ICE one would make enough of a difference in the outcome of the experiment to dominate other sources of error in the setup. The collision between a small, relatively speaking light and hard, stone and the fairly heavy, also hard, steel rotor of a lawn mower with substantial inertia, is as near to the idealistic elastic collision as dammit. Without doing the math, my feeling is that if you did so, you'd come up with the answer that it didn't matter anyway. So you'd have to compare the torque curves at the precise operating (speed/load) where the stone was hit. (Indeed, that's why many internal combustion engines has an electric motor to start it). torque as a function of angular velocity ("revs") is very different between an electric motor and an internal combustion engine. Now, the main problem with the lawn mower example is that the torque curves, i.e. Of course, going up a hill your engine/motor's power output better be greater than the work you're doing, otherwise you've made a perpetum mobile You need enough output torque that when its converted to a force at the wheel/road surface, that force is sufficient to overcome the force due to other losses (wind resistance, or work due to going up hill). In fact, it's torque that maintains speed as well. a car, you can't say that "horse power" maintains speed. So while you need torque to accelerate e.g. Power (weather measured in HP or Watts) for a rotating machine is simply the torque multiplied by the angular velocity.
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