# Answer to Question #102548 in Mechanics | Relativity for Jarred

Question #102548
25lb brick falls 4ft what is the force of impact?
1
2020-02-10T09:08:29-0500

Solution. According to the conditions of the problem m=11.3398kg and h=1.2192m. Using the law of conservation of mechanical energy for the initial and final positions, we write

"mgh=\\frac{mv^2}{2}"

Hence velocity at the time of impact is

"v=\\sqrt{2gh}"

where h is height; g=9.8 m/s^2 is gravitaty acceleration.

On the other hand, using the law of conservation of momentum, we obtain

"m\\Delta v=Ft"

where ∆v is velocity change; F is force of impact; t is impact time. The equations of motion of a brick can be written

"h=\\frac{gt^2}{2} \\implies t=\\sqrt{\\frac{2h}{g}}"

Сombining the equations we get

"F=\\frac{m\\Delta v}{t}=\\frac{m\\sqrt{2gh}}{\\sqrt{\\frac{2h}{g}} }=mg"

"F=11.3398\\times 9.8\\approx 111.13N"

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