What is the initial velocity of a ball that is thrown downward from the rooftop of a 12-m building and falls to the ground after 1.14 s. Ignore air friction. How will I solve this?

Expert Answers

An illustration of the letter 'A' in a speech bubbles

We can solve this by using the equation of motion.

`s = ut + 1/2 at^2`

where s is the distance traveled, u is the initial velocity, t is the time duration and a is the acceleration. 

In this case, the distance traveled (s) is 12 meters. The time taken by the ball to fall down is 1.14 seconds and the acceleration is due to Earth's gravity and is, hence, equal to acceleration due to gravity, g. 

Thus, s = 12 m, t = 1.14 s and a = g = 9.81 m/s^2

Substituting these values into the equation of motion, we get:

12 = 1.14u + 1/2 (9.81) (1.14)^2

Solving the equation, we get, u = 4.94 m/s.

Thus, the ball was thrown with an initial velocity of 4.94 m/s.

Note that resistance by air has been neglected in this case.

Hope this helps. 

Approved by eNotes Editorial Team
Soaring plane image

We’ll help your grades soar

Start your 48-hour free trial and unlock all the summaries, Q&A, and analyses you need to get better grades now.

  • 30,000+ book summaries
  • 20% study tools discount
  • Ad-free content
  • PDF downloads
  • 300,000+ answers
  • 5-star customer support
Start your 48-Hour Free Trial