First slide

Work Energy Theorem

Question

An open knife edge of mass M is dropped from a height 'h' on a wooden floor. If the blade penetrates a distance 's' into the wood, the average resistance offered by the wood to the blade is :

Moderate

A

Mg
B

$\large Mg\left (1+\frac hs \right )$
C

$\large Mg\left (1-\frac hs \right )$
D

$\large Mg\left (1+\frac hs \right )^2$

Solution

When the front end of the knife arrives at A, its kinetic energy $\frac 12Mv^2=Mgh$ . During the course of penetration net vertically downward force acting on the knife = (Mg - R).
By work energy theorem $(Mg-R)S=0-\frac 12mv^2\Rightarrow R=Mg\left ( 1+\frac hs \right )$

Get Instant Solutions

When in doubt download our app. Now available Google Play Store- Doubts App

Recieve an sms with download link

Doubts App

OR

SCAN ME

Doubts App

Doubts App