Question

AB is a frictionless inclined surface making an angle of ${30}^0$ with horizontal. A is $6.3m$ above the ground while B is $3.8m$ above the ground. A block slides down from A, initially starting from rest. Its velocity on reaching B is:

• A. $7m{s}^{-1}$
• B. $14m{s}^{-1}$
• C. $7.4m{s}^{-1}$
• D. $4.9m{s}^{-1}$

Answer 1

Answer: (A)

$7m{s}^{-1}$

1) $M.E\left(A\right)=M.E\left(B\right)$
$M.E\left(A\right)=P.E\left(A\right)$ & $M.E\left(B\right)=K.E\left(B\right)+P.E\left(B\right)$
$\Rightarrow mgh\left(A\right)=mgh\left(B\right)+\frac{1}{2}mV{{}_B}^2$
$V{{}_B}^2=g(6.3-3.8)\times 2$
$V{{}_B}^2=g\times 2.5\times 2$
$V_B=7m/s$