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

[RachelT]

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

 

[CWatters]

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.

 

[RachelT]

Thankyou

 

[CWatters]

Oh I see you mean two decimal places?

 

[RachelT]

Haha yeah 2dp, that's the English way (guessing your not English?)

 

[CWatters]

Yes English (but was still awake at 2am last night so not on best form today :-).