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What force is exerted on the windscreen?

  • Thread starter looi76
  • Start date
  • #1
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Homework Statement


A car is driving through a rainstorm. Each raindrop of mass [tex]0.00005kg[/tex] hits the windscreen with velocity of [tex]16 ms^{-1}[/tex]. If [tex]500[/tex] raindrops hit the glass and run down the windscreen each second without bouncing, what force is exerted on the windscreen?

Homework Equations



Force = Mass x Acceleration

Momentum = Mass x Velocity

Inelastic Collisions:
[tex]m_1u_1 + m_2u_2 = (m_1+m_2)v[/tex]

The Attempt at a Solution



[tex]m = 5.0 \times 10^{-5}kg \ , \ u = 16ms^{-1}[/tex]

don't know how to start, need help!
 
Last edited:

Answers and Replies

  • #2
275
2
The equations you gave are correct; but also remember that F = change in momentum / change in time.
Make sure you keep track of your units, and a force needs to end up being kg*m/s^2.
 
  • #3
81
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Can someone please explain. Still, I don't know how to start =(
 
  • #4
mgb_phys
Science Advisor
Homework Helper
7,774
12
As lzkelley said, force is change in momentum / time and momentum is mass * velocity.
The rain drop is accelerated to the speed of the car by the windscreen and so pushes on the widnscreen with a force equal to the raindrops mass * change in velocity.

Assuming the drop is falling vertically, you have the change in velocity, you know the total mass of raindrops falling per second so you have the force.
 

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