Question

Two block of masses $40kg$ and $20kg$ are connected by a wire that has a linear mass density of $1g/m$. These blocks are being pulled across horizontal frictionless floor by horizontal force $F$ that is applied to $20kg$ block. A transverse wave travel on the wave between the blocks with a speed of $400m/s$ (relative to the wire). The mass of the wire is negligible compared to the mass of the blocks The magnitude of $F$ is

• A. $160N$
• B. $240N$
• C. $320N$
• D. $400N$

Answer 1

Answer: (B)

$240N$

$\begin{array}{c}v=\sqrt{\frac{T}{M}}\\ \Rightarrow 400=\sqrt{\frac{T\times 1000}{1}}\\ \Rightarrow 16\times {10}^4=7\times 1000\\ \Rightarrow T=160N\\ Now,\\ T=40a\\ \Rightarrow a=\frac{160}{40}=4m/s^2\\ \Rightarrow F-T=20a\\ \Rightarrow F-160=80\\ \Rightarrow F=240N\\ Hence,\\ optionBiscorrectanswer.\end{array}$