Imagine that during a hailstorm, hailstones with an average mass of 9 g and an a

Question

Imagine that during a hailstorm, hailstones with an average mass of 9 g and an average vertical velocity of 45 m/s hit the roof of your car at a rate of 140 hits per second per square meter; and assume that they bounceelastically off the roof.

What is the approximate pressure, in Pascal, that these hailstones exert on your roof? Assume the velocity of a hailstone is exactly reversed when it bounces off your roof.  Hint: Use the impulse-momentum theorem which states that Impulse = Force x Time = Change in Momentum.

Explanation / Answer

impulse due to each hail = 2 * mass * velocity = 2 * 0.009 * 45 = 0.81 N-s

so.. Force on roof = impulse due to each * no. of hits per second = 140 * 0.81 = 113.4 N

so.. pressure = force / area = 113.4 / 1 = 113.4 Pa

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