Home › UP Board Class 10 › Mathematics › A girl of height $90\text{ cm}$ walks away from …
A girl of height $90\text{ cm}$ walks away from the base of a lamp-post at a speed of $1.2\text{ m/s}$. If the lamp-post is $3.6\text{ m}$ high, how far is the girl from the lamp-post after 4 seconds? 
A$3.6\text{ m}$
B$4.8\text{ m}$
C$5.2\text{ m}$
D$6.0\text{ m}$
Answer & Solution
Correct answer: B. $4.8\text{ m}$
Distance travelled $=$ speed $\times$ time $=1.2\times 4=4.8\text{ m}$. So after 4 seconds, the girl is $4.8\text{ m}$ from the lamp-post.
Related questions
What is the derivative of $x^x$ for $x>0$?If $y=x^{\tan^{-1}x}$, then $\dfrac{dy}{dx}$ equalsThe derivative of $ in^{-1}x$ isThe derivative of $\cos^{-1}x$ isWhat is $\dfrac{d}{dx}(\tan^{-1}x)$?If $y=\dfrac{1}{x^n}$, then $\dfrac{dy}{dx}$ isWhich identity is correct?For the expression $ qrt{1-x^2}$, a useful trigonometric substitution is