what force is exerted on the windscreen?

• May 14th 2008, 11:36 AM
looi76
what force is exerted on the windscreen?
Question:
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?

Attempt:

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

don't know how to start, need help!
• May 14th 2008, 06:55 PM
topsquark
Quote:

Originally Posted by looi76
Question:
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?

Attempt:

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

don't know how to start, need help!

Let's "ramble" this one out step by step.

500 raindrops per second means that you have 500 times 0.00005 kg striking the windshield per second.

So in one second 0.0250 kg of mass at 16 m/s strikes the windshield. This creates a change in momentum of 0.4 kg m /s in that one second. This is, in turn, equal to the impulse exerted on the windshield in one second: 0.4 Ns. Thus the force on the windshield is 0.4 N s / 1 s = 0.4 N.

-Dan
• May 14th 2008, 07:50 PM
mr fantastic
Quote:

Originally Posted by topsquark
Let's "ramble" this one out step by step.

500 raindrops per second means that you have 500 times 0.00005 kg striking the windshield per second.

So in one second 0.0250 kg of mass at 16 m/s strikes the windshield. This creates a change in momentum of 0.4 kg m /s in that one second. This is, in turn, equal to the impulse exerted on the windshield in one second: 0.4 Ns. Thus the force on the windshield is 0.4 N s / 1 s = 0.4 N.

-Dan

I think that the velocity of the car and the angle at which the raindrops hit the windscreen are important pieces of missing infromation ..... Assumptions can be made about the latter - nevertheless the velocity of the car will still be a relevant factor .....
• May 14th 2008, 08:03 PM
topsquark
Quote:

Originally Posted by mr fantastic
I think that the velocity of the car and the angle at which the raindrops hit the windscreen are important pieces of missing infromation ..... Assumptions can be made about the latter - nevertheless the velocity of the car will still be a relevant factor .....

Good points on both comments. (Bow)

-Dan