What force is exerted on the windscreen?

[looi76]

Homework Statement

A car is driving through a rainstorm. Each raindrop of mass $$0.00005kg$$ hits the windscreen with velocity of $$16 ms^{-1}$$. If $$500$$ 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:
$$m_1u_1 + m_2u_2 = (m_1+m_2)v$$

The Attempt at a Solution

$$m = 5.0 \times 10^{-5}kg \ , \ u = 16ms^{-1}$$

don't know how to start, need help!

 

[lzkelley]

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.

 

[looi76]

Can someone please explain. Still, I don't know how to start =(

 

[mgb_phys]

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.