Since the kinematic equations include four variables, you only need to know three of the variables to solve for the unknown. Therefore you answer is 3.
To solve using one of the kinematic equations a person must know the value of three variables.
The Equation of Kinematics shown below,
[tex]v=u+at\\ \\ s=ut+\frac{1}{2}at^{2} \\ \\ v^{2}=u^{2}+2as [/tex]
Where u is initial velocity, v is final velocity, a is acceleration and t is time , s is distance.
From observing above equations, there are 4 variables present in all equation.
Hence, To solve using one of the kinematic equations a person must know the value of three variables.
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