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3 years ago

10

A 12-kg lead brick falls from a height of 1.9 m. (c) The brick falls onto a carpet, 2.0 cm thick. Assuming the force stopping it

is constant, find the average force the carpet exerts on the brick.

1 answer:

Genrish500 [490]3 years ago

8 0

Answer:

F = -11199.63 N

Explanation:

given,

mass of the brick = 12 Kg

height of the fall, h = 1.9 m

thickness of the carpet = 2 cm = 0.02 m

average force = ?

velocity of brick just before hitting mat

$v = \sqrt{2gh}$

$v =\sqrt{2\times 9.81\times 1.9}$

v = 6.11 m/s

velocity of brick just before hitting ground= 6.11 m/s

final velocity = 0 m/s

using equation of motion for acceleration calculation.

v² = u² + 2 a s

0² = 6.11² + 2x a x 0.02

$a = -\dfrac{6.11^2}{0.04}$

a =-933.3025 m/s²

now, average force is equal to

F = m a

F = 12 x (-933.3025)

F = -11199.63 N

negative sign represent the decelerating force.

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(c)Distance, s=268.8m

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<u>Explanation</u>:

<u>Given</u>:

Distance travelled = 40 miles

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(A) The average velocity in kilometres/hour

Converting 40 miles into km ,

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40 miles = 40 x 1.60934

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similarly converting 30 minutes into hours

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Average velocity = $64.3738 \times 2$

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(B) If the car weighs 1.5 tons, what is its If the car weighs 1.5 tons, what is its kinetic energy in joules (Note: you will need to convert your velocity to m/s)? in joules (Note: you will need to convert your velocity to m/s)?

Converting 1.5 tons into kg we get

1 ton = 1000 kg

so 1.5 ton =1500 kg

converting velocity to m/s

$128.74 \times \frac{5}{18}$

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kinetic energy K= $\frac{1}{2}mv^2$

Substituting the values,

K= $\frac{1}{2}1500(35.75)^2$

K= $\frac{1}{2}1500(1278.06)$

K= $\frac{1500 \times (1278.06)}{2}$

K= $\frac{1917093.75}{2}$

K=958546.875 Joule---------------------------------------------(2)

(c)When the driver applies the brake, it takes 15 seconds to stop. How far does the car travel (in meters) while stopping

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Substituting the known values,

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Using the formula

v=u +at

re arranging the formula we get,

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Substituting the values

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$a = \frac{- 35.75}{15}$

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Now substituting 4 in 3 we get

$s=566.25+\frac{(225( - 2.38)}{2}$

$s=566.25+\frac{-535.5}{2}$

$s=536.25-267.75$

s=268.8m--------------------------------------------------------------(5)

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