# Finding Final Speed Using

Finding Final Speed Using Work

A person pushes with a horizonal 25N force over a distance of 1.2m on a 4.5kg crate, intially at rest on a frictionless surface. What is the final speed of the crate?

heres my data list..

F=25N
delta d=1.2m
m=4.5kg
v1=0
v2=?
theta=0 degrees

i used the W=fxdeltadxcos(theta) formula to find out the work done was 30J.. but once i have work i dont no what to find next to find the final speed..

Last edited:

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There are two ways of approach. One is using the constant accleration equation

(v2)^2=(v1)^2+2as

where a is the acceleration of the crate and s is the displacement caused by the accleration, i.e.

v1 = 0, a = F/m (Newton's Second Law) = 25/4.5 = 50/9, s = 1.2, so

v2 = sqrt (2.4*50/9) = sqrt (120/9 ) = sqrt (120)/3

The other is to find the work done by the force = F.d = 25*1.2 = 30J
and then say this is the additional kinetic energy given to the crate. Since the crate was at rest, we can say

0.5*m*(v2)^2 = 30
v2 = sqrt ( 60/4.5 ) = sqrt (120/9) = sqrt (120)/3

rock.freak667
Homework Helper
What is the work done by the force converted into? (If it is moving what kind of energy does it have?)

Energy by virtue of its motion is called kinetic energy, and kinetic energy is given by the formula K.E. = 0.5mv^2 where m is the mass of the body and v is the velocity.