KCET · Physics · Laws of Motion
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 \(\mathrm{g}=10 \mathrm{~ms}^{-2}\) )
- A 4.4 kg
- B 1.2 kg
- C 1.0 kg
- D 2.2 kg
Answer & Solution
Correct Answer
(D) 2.2 kg
Step-by-step Solution
Detailed explanation
Friction must be kinetic
\(\begin{aligned}
& \mathrm{a}=\frac{\mathrm{v}-\mathrm{u}}{\mathrm{t}}=\frac{20-0}{3}=\frac{20}{3} \mathrm{~m} / \mathrm{s}^2 \\
& \mathrm{~F}-\mathrm{f}_{\mathrm{k}}=\mathrm{ma}
\end{aligned}\)
\(\begin{aligned} & 20-0.25 \mathrm{~m} \times 10=\mathrm{m} \times \frac{20}{3} \\ & \mathrm{~m}=2.2 \mathrm{~kg}\end{aligned}\)
\(\begin{aligned}
& \mathrm{a}=\frac{\mathrm{v}-\mathrm{u}}{\mathrm{t}}=\frac{20-0}{3}=\frac{20}{3} \mathrm{~m} / \mathrm{s}^2 \\
& \mathrm{~F}-\mathrm{f}_{\mathrm{k}}=\mathrm{ma}
\end{aligned}\)
\(\begin{aligned} & 20-0.25 \mathrm{~m} \times 10=\mathrm{m} \times \frac{20}{3} \\ & \mathrm{~m}=2.2 \mathrm{~kg}\end{aligned}\)
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