Answer:
Constant
Step-by-step explanation:
Here's the definition of the noun:
"A situation that does not change"
In this case the situation is the speed of the object.
If you'd like to go into further detail, let's move away from English and jump into Physics. The question asked for "object's force" - keyword: 'force'. What's the formula for force? F = m * a.
F = Force, m = mass, a = acceleration.
Okay well, the question said only the speed changes and doesn't mention the mass changing so if the mass changes the force won't be constant. However, if the mass doesn't change (constant), we can continue to acceleration.
The formula for acceleration is (I think) m/s^2, that's metres over time, squared. As we know from English class; the speed is constant and thus the square of that speed is also constant - therefore the acceleration is constant.
Now, putting them together, assuming the mass is constant, we know the acceleration is constant so the force has to be constant. Case closed.
*mic drops, this was a waste of time*