The force applied to the physics cart is manipulated. this is the variable. the cart accelerates due to the force applied to the cart. acceleration is therefore the variable. a "constant" is a parameter that stays the same regardless of the variables. one parameter of the cart that is held constant is the

As per Newton's II law we know that

now if we apply some force F on an object then as per Newton's II law

if Force is variable then we will have variable acceleration accordingly

now we can say

so here acceleration will vary with same proportionality as we will vary the value of force

so here the constant parameter is MASS(M)

so in the above case mass will remain constant

i don't understand is there any other way you can rephrase it plz let me know in the comments and i will do it.

explanation:

c. newton's third law of motion