Question

A ball is thrown upward with an initial velocity of $100{\text{ms}}^{-1}$. Find the height of the ball after $15\text{s}$. Take $g=10{\text{ms}}^{-2}$

• A. $375\text{m}$
• B. $425\text{m}$
• C. $395\text{m}$
• D. $275\text{m}$

Answer 1

The correct option is A $375\text{m}$

Here, $u=100{\text{ms}}^{-1},a=-g=-10{\text{ms}}^{-2}$
At highest point, $v=0$
As $v=u+gt\therefore 0=100-10\times t$
$\therefore$ Time taken to reach highest point,
$t=\frac{100}{10}=10\text{s}$
The ball will return to the ground at $t=20\text{s}$
Corresponding velocity - time graph of the ball is shown in
Height attained after $15\text{s}=\text{Area of}\Delta AOB+\text{Area of}\Delta BCD$
$=500+\frac{1}{2}(15-10)\times (-50)=500-125=375\text{m}$