A stone is allowed to fall from the top of a tower $100\ m$ high and at the same time another stone is projected vertically upwards from the ground with a velocity of $25\ m/s$. Calculate when and where the two stones will meet.
For stone A: When the stone from the top of the tower is thrown,
Initial velocity $u_A=0$
Distance traveled $=x$
Time taken $=t$
Therefore,
Height, $h=(100 – x)$
Here, $g=10\ m/s^2$ [As the stone is falling down]
We know that,
$h=ut+\frac{1}{2}gt^2$
On substituting the values in the above equation
$(100-x)=0\times t+\frac{1}{2}\times 10\times t^2$
Or $(100-x)=5t^2$ .......$(i)$
For stone B: for stone projected vertically upwards:
Height, $h=x$
Initial velocity, $u_B=25\ m/s$
Time, $t=?$
$g=-10\ m/s^2$ [Because the stone is going up]
On using, $s=ut+\frac{1}{2}gt^2$
Or $x=25t+\frac{1}{2}(-10)t^2$
Or $x=25t-5t^2$
On adding the above equations We get
$100=25t$
or $t=\frac{100}{25}=4\ s$
After $4\ second$, the two stones A and B will meet.
On putting the value $t=4\ s$ in $(i)$
$100-x=5t^2$
Or $x=100-5t^2$
Or $x=100-5\times4^2$
Or $x=100-80$
Or $x=20\ m$
So, after $4\ seconds$, two stones meet at a distance of $20\ m$ from the ground.
Related Articles
- A stone is released from the top of a tower of height $19.6\ m$. Calculate its final velocity just before touching the ground.
- A stone is thrown vertically upwards with a speed of 20 m/s. How high will it go before it begins to fall? $(g=9.8\ m/s^2)$
- A piece of stone is thrown vertically upwards. It reaches the maximum height in 3 seconds. If the acceleration of the stone be $9.8\ m/s^2$ directed towards the ground, calculate the initial velocity of the stone with which it is thrown upwards.
- A stone is thrown vertically upward with an initial velocity of $40\ m/s$. Taking $g=10\ m/s^2$, find the maximum height reached by the stone. What is the net displacement and the total distance covered by the stone?
- A stone is dropped from the top of a tower $500\ m$ high into a pond of water at the base of the tower. When is the splash heard at the top? Given, $g=10\ ms^{-2}$ and speed of sound $=340\ ms^{-1}$.
- A stone falls from a building and reaches the ground 2.5 seconds later. How high is the building? $(g=9.8\ m/s^2)$
- 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? $(g=10\ m/s^2)$
- A tower stands vertically on the ground. From a point on the ground, \( 20 \mathrm{~m} \) away from the foot of the tower, the angle of elevation of the top of the tower is \( 60^{\circ} \). What is the height of the tower?
- The angles of elevation of the top of a tower from two points at a distance of 4 m and 9 m from the base of the tower and in the same straight line with it are complementary. Prove that the height of the tower is 6 m.
- A car of mass $1000\ kg$ is moving with a velocity of $10\ m/s$. If the velocity-time graph for this car is a horizontal line parallel to the time axis, then the velocity of the car at the end of $25\ s$ will be:a). 40 m/s b). 25 m/sc). 10 m/s d). 250 m/s
- A ball is gently dropped from a height of $20\ m$. If its velocity increases uniformly at the rate of $10\ m s^{-2}$, with what velocity will it strike the ground? After what time will it strike the ground?
- The angles of elevation of the top of a tower from two points at a distance of \( 4 \mathrm{~m} \) and \( 9 \mathrm{~m} \) from the base of the tower and in the same straight line with it are complementary. Prove that the height of the tower is \( 6 \mathrm{~m} \).
- Draw a velocity versus time graph of a stone thrown vertically upwards and then coming downwards after attaining the maximum height.
- The angle of elevation of the top of tower, from the point on the ground and at a distance of 30 m from its foot, is 30o. Find the height of tower.
- The angle of the elevation of the top of vertical tower from a point on the ground is 60°. From another point 10 m vertically above the first, its angle of elevation is 30°. Find the height of the tower.
Kickstart Your Career
Get certified by completing the course
Get Started