A ball is thrown horizontally from the top of tower100 m high, with sp

1.	A ball is thrown horizontally from the top of tower100 m high, with speed 10 m/s. After 2 seconds offall, gravity disappears. Then total time taken by ballto reach the ground is (g = 10 m/s2)(1) 10 s(2) 8s(3) 6 s(4) 4 s
Answer» Answer: Option (3) 6s Explanation: Given, The height of the tower = 100 m Initial HORIZONTAL speed = 10 m/s Ball is THROWN horizontally from the top of the tower therefore its initial vertical speed will be zero Thus using the second equation of motion The vertical distance h covered in 2 seconds $h=\frac{1}{2}gt^2$ or, $h=\frac{1}{2}\times 10\times 2^2=20$ m Therefore the height left = 100 - 20 = 80 m The vertical velocity after 2 seconds using the first equation of motion $v=0+gt$ $\implies v=10\times2=20$ m/s Since the gravity disappears after 2 seconds therefore there will be no acceleration in the vertical direction TIME taken to cover 80 m distance = distance/velocity = 80/20 = 4 seconds Therefore, TOTAL time taken by the ball to reach the ground = 2 + 4 =6 seconds

A ball is thrown horizontally from the top of tower100 m high, with speed 10 m/s. After 2 seconds offall, gravity disappears. Then total time taken by ballto reach the ground is (g = 10 m/s2)(1) 10 s(2) 8s(3) 6 s(4) 4 s

Answer»

Answer:

Option (3) 6s

Explanation:

Given,

The height of the tower = 100 m

Initial HORIZONTAL speed = 10 m/s

Ball is THROWN horizontally from the top of the tower therefore its initial vertical speed will be zero

Thus using the second equation of motion

The vertical distance h covered in 2 seconds

$h=\frac{1}{2}gt^2$

or, $h=\frac{1}{2}\times 10\times 2^2=20$ m

Therefore the height left = 100 - 20 = 80 m

The vertical velocity after 2 seconds

using the first equation of motion

$v=0+gt$

$\implies v=10\times2=20$ m/s

Since the gravity disappears after 2 seconds

therefore there will be no acceleration in the vertical direction

TIME taken to cover 80 m distance = distance/velocity

= 80/20 = 4 seconds

Therefore, TOTAL time taken by the ball to reach the ground = 2 + 4 =6 seconds