Question

Before starting this problem, review Conceptual Example 3 in your text. Suppose that the hail described there comes straight down at a mass rate of m/?t = 0.030 kg/s and an initial velocity of v0 = -15 m/s and strikes the roof perpendicularly. Suppose that the hail bounces off the roof of the car with a velocity of +15 m/s. Ignoring the weight of the hailstones, calculated the force exerted by the hail on the roof. __________N

Answer 1

Answer:

0.9 N

Explanation:

The force exerted on an object is related to its change in momentum by:

$F=\frac{\Delta p}{\Delta t}$

where

F is the force exerted

$\Delta p$ is the change in momentum

$\Delta t$ is the time interval

The change in momentum can be rewritten as

$\Delta p = m(v-u)$

where

m is the mass

u is the initial velocity

v is the final velocity

So the formula can be rewritten as

$F=\frac{m(v-u)}{\Delta t}$

In this problem we have:

$\frac{m}{\Delta t}=0.030 kg/s$ is the mass rate

$u=-15 m/s$ is the initial velocity

$v=+15 m/s$ is the final velocity

Therefore, the force exerted by the hail on the roof is:

$F=(0.030)(+15-(-15))=0.9 N$