- Data Structure
- Networking
- RDBMS
- Operating System
- Java
- MS Excel
- iOS
- HTML
- CSS
- Android
- Python
- C Programming
- C++
- C#
- MongoDB
- MySQL
- Javascript
- PHP
- Physics
- Chemistry
- Biology
- Mathematics
- English
- Economics
- Psychology
- Social Studies
- Fashion Studies
- Legal Studies
- Selected Reading
- UPSC IAS Exams Notes
- Developer's Best Practices
- Questions and Answers
- Effective Resume Writing
- HR Interview Questions
- Computer Glossary
- Who is Who
A stone is dropped from a height of 20 m.
(i) How long will it take to reach the ground?
(ii) What will be its speed when it hits the ground? $(g=10\ m/s^2)$
Given: Initial velocity $u=0$
Height $h=20\ m$
Gravitational acceleration $g=10\ m/s^2$
To do: (i). To find how long will it take to reach the ground.
(ii). To find its speed when it hits the ground.
Solution: Let $v$ be the final velocity when it hits the ground and $t$ be the time taken to reach the ground.
On using the equation of the motion, $v^2=u^2+2gh$
$v^2=0+2\times10\times20$
Or $v^2=400$
Or $v=\sqrt{400}$
Or $v=20\ m/s$
On using the first equation of motion $v=u+gt$
$20=0+10\times t$
Or $10t=20$
Or $t=\frac{20}{10}$
Or $t=2\ s$
Therefore, it will take $2\ s$ to reach the ground and its speed when it hits the ground is $20\ m/s$.