It can't be less than 250 N or the cart wouldn't move at all. That means there is only 1 answer. It's between not enough info or 250 N. The answer is 250 N. If it was any more, there would be acceleration.
A "heating curve" is a graph that shows the temperature of the substance
against the amount of heat you put into it.
For most of the graph, as you'd expect, the temperature goes up as you
add heat, and it goes down as you take heat away. BUT ... While the
substance is changing state, its temperature doesn't change even though
you're putting heat in or taking heat out.
So that part of the graph is a horizontal line.
So that we do not contaminate it with microorganisms or garbage or other human stuff.
If you were given distance & period of time, you would be able to calculate the speed.
Hope this helps!
