Question

what will be the change in acceleration of a sliding block,if its mass is doubled while a constant force is acting on it

Answer 1

Let m be the mass of object , F be the constant force applied on it produce acceleration 'a' and $\mu$ be kinetic friction between surface and mass.
Force of friction ,f = $\mu mg$
Force that produce acceleration, F-f = ma- $\mu mg$ = $m\left(a-\mu g\right)$ ---(1)
Now , mass is double,
Force that produce acceleration, F-f' = ma'- $2\mu mg$ = $m\left(a-2\mu g\right)$ ---(2) subtracting (1) from (2)

$$\begin{gathered} m\left(a\text{'}-a\right)-\mu mg=m\left(a-2\mu g-a+\mu g\right) \\ m\left(a\text{'}-a-\mu g\right)=-m\mu g \\ a\text{'}-a=0 \end{gathered}$$

change in acceleration is zero. Acceleration remains uniform.