What Is the Speed of a Tennis Ball Dropped from 20m?

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Homework Help Overview

The discussion revolves around calculating the speed of a tennis ball dropped from a height of 20 meters using the principles of potential energy (PE) and kinetic energy (KE). The original poster presents their attempt at solving the problem using the relevant equations.

Discussion Character

  • Exploratory, Mathematical reasoning

Approaches and Questions Raised

  • The original poster attempts to equate potential energy and kinetic energy to find the speed of the tennis ball. Some participants question the clarity of the notation used for the final answer, specifically regarding the mention of "2dp" (two decimal places).

Discussion Status

The discussion is ongoing, with participants clarifying terminology and notation. There is no explicit consensus on the correctness of the original poster's calculations, but there is engagement in understanding the presentation of the answer.

Contextual Notes

Participants note the use of different conventions in expressing numerical precision, which may reflect cultural differences in mathematical notation.

RachelT
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Homework Statement



Using formulae for PE and KE, find the speed that a tennis ball hits the ground when dropped from 20m.

Homework Equations



m x g x h and 1/2 x m x v^2

The Attempt at a Solution



PE=KE

Mgh = 1/2mv^2 (masses cancel out)
9.8 x 20.= 1/2 v^2
196 = 1/2 v^2
196/ 1/2 = v^2
392 = v^2
V = 19.8(2dp) ms-1

Am I correct? Thankyou
 
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yes but what is the (2dp) in ..

V = 19.8(2dp) ms-1

Answer should just be

V = 19.8 ms-1


Allways better to rearrange the equation before putting in the numbers.
 
Thankyou
 
Oh I see you mean two decimal places?
 
Haha yeah 2dp, that's the English way (guessing your not English?)
 
Yes English (but was still awake at 2am last night so not on best form today :-).
 

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