Checking a question involving impact/impulse forces


by emilypearson
Tags: checking, forces, impact or impulse, involving
emilypearson
emilypearson is offline
#1
Jan20-12, 09:44 AM
P: 7
1. The problem statement, all variables and given/known data
A ceramic pot of mass 0.5 kg will break if it strikes the floor with an impact force equal
to, or greater than, 20 N. The collision lasts for 0.05 s. Find the minimum vertical height
from which, if dropped from rest, the pot will break upon impact with the floor (you
may ignore air resistance).

2. Relevant equations
Impulse=FΔt=Pfinal-Pinital
Fd=ΔKinetic energy
PE=mgh
KE=1/2mv2

3. The attempt at a solution
At a height h, the object has KE=0 and PE=mgh=0.5gh
At impact, the object has KE=1/2mv2=0.25v2 and PE=0
FΔt=Pf-Pi
However Pi=0 as the velocity is 0.
equation 1: 20*0.05=Pf=mv=0.5v
to find v:
1/2mv2=mgh
rearrange to give v=√2gh
back into equation 1:
1=0.52*2gh
h=1/0.52*2*9.81
h=0.2m

Is this correct? That doesn't seem big enough in order for the pot to break (thinking in real world terms)
Phys.Org News Partner Science news on Phys.org
Lemurs match scent of a friend to sound of her voice
Repeated self-healing now possible in composite materials
'Heartbleed' fix may slow Web performance
technician
technician is offline
#2
Jan20-12, 10:20 AM
P: 1,506
You need to use the fact that force = change in momentum per second.
They give you the force so you need to get momentum information
Do you know how?
emilypearson
emilypearson is offline
#3
Jan20-12, 10:25 AM
P: 7
That's what I attempted to do with the Pf-Pi with P being momentum (mv) ... is that not the right equation?

technician
technician is offline
#4
Jan20-12, 10:34 AM
P: 1,506

Checking a question involving impact/impulse forces


You are correct and if you look at your equation 1 you see that v = 2 m/s ?
So 2 = √2gh.
emilypearson
emilypearson is offline
#5
Jan20-12, 11:03 AM
P: 7
Perfect - thanks :)


Register to reply

Related Discussions
Two Impulse & Impact Problems! Need Help! Introductory Physics Homework 1
Statics Question involving forces and moments Engineering, Comp Sci, & Technology Homework 2
IB 11 Question: Circular Acceleration Problem Involving Forces Introductory Physics Homework 5
IB 11 Question: ANOTHER Circular Acceleration Problem Involving Forces Introductory Physics Homework 1
momentum, impulse, impact Introductory Physics Homework 1