question_answer

  A ball is thrown upwards from the ground of a tower with a speed of 20 m/s. There is a window in the tower at the height of 15 m from the ground. How many times and when will the ball pass the windows? (Take g= 10 m/s2)

Answer:

                  Initial velocity, u = 20 m/s Maximum height the ball will reach, h = ? Using equation v2 = u2 + 2gh ( At maximum height, v = 0)            (1) This means ball will reach the height of 20 m and comes back. It will pass the window two times.                                                                               (1/2) Now to calculate the time ball will take to reach 15m heights Using equations,                                                                                                              Thus, ball will pass the window at 1 second and 3 seconds respectively.