Q122 / 180 · KCET 2025 · Physics

A block of certain mass is placed on a rough floor. The coefficients of static and kinetic friction between the block and the floor are 0.4 and 0.25 respectively. A constant horizontal force $\mathrm{F}=20 \mathrm{~N}$ acts on it so that the velocity of the block varies with time according to the following graph. The mass of the block is nearly (Take $\mathrm{g}=10 \mathrm{~ms}^{-2}$ ) Figure

  • A
    4.4 kg
  • B
    1.2 kg
  • C
    1.0 kg
  • Correct answer
    D
    2.2 kg

Solution

Friction must be kinetic $\begin{aligned} & \mathrm{a}=\frac{\mathrm{v}-\mathrm{u}}{\mathrm{t}}=\frac{20-0}{3}=\frac{20}{3} \mathrm{~m} / \mathrm{s}^2 \\ & \mathrm{~F}-\mathrm{f}_{\mathrm{k}}=\mathrm{ma} \end{aligned}$ $\begin{aligned} & 20-0.25 \mathrm{~m} \times 10=\mathrm{m} \times \frac{20}{3} \\ & \mathrm{~m}=2.2 \mathrm{~kg}\end{aligned}$

Hence, the correct answer is option: 'D'.

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