# NCERT Question 17 - Chapter 10 Class 9 - Gravitation

Last updated at April 16, 2024 by Teachoo

NCERT Questions

NCERT Question 1

NCERT Question 2 Important

NCERT Question 3

NCERT Question 4

NCERT Question 5 Important

NCERT Question 6 Important

NCERT Question 7

NCERT Question 8 Important

NCERT Question 9

NCERT Question 10

NCERT Question 11 Important

NCERT Question 12 Important

NCERT Question 13 Important

NCERT Question 14 Important

NCERT Question 15

NCERT Question 16

NCERT Question 17 Important You are here

NCERT Question 18 Important

NCERT Question 19 Important

NCERT Question 20 Important

NCERT Question 21 Important

NCERT Question 22

Class 9

Chapter 10 Class 9 - Gravitation

Last updated at April 16, 2024 by Teachoo

NCERT Question 17 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. Distance moved by Stone 1 Distance moved by Stone 2 Let Stone 1 be the stone that is dropped from tower And stone 2 be the stone that is projected upwards Let the two stones meet at time = t seconds Finding distanced moved by both stones in time t seconds Distance moved by Stone 1 Initial velocity = u1 = 0 m/s Acceleration = a1 = g = 10 m/s2 (Positive acceleration as it is moving down) We know u1, a1 and t, Distance moved by Stone 2 Initial velocity = u2 = 25 m/s Acceleration = a2 = −g = −10 m/s (Negative acceleration as it is going up) We know u2, a2 and t, Finding distance covered by 2nd equation of motion s1 = u1t + 1/2 a1t2 s1 = 0 × t + 1/2 (10) t2 s1 = 5t2 Finding distance covered by 2nd equation of motion s2 = u2t + 1/2 a2t2 s2 = 25t + 1/2 (−10) t2 s2 = 25t − 5t2 Now, Total distance covered by both stones = 100 m s1 + s2 = 100 m 5t2 + 25t − 5t2 = 100 25t = 100 t = 100/25 t = 4 s At t = 4s, s1 = 5t2 = 5 × 42 = 5 × 16 = 80 m s2 = 25t − 5t2 = 25 × 4 − 5 × 42 = 100 – 80 = 20 m Therefore, The stones will meet when time is 4 seconds and Distance is 80 m from the top