Physics Problem, cant find mistake, okz help

[Ion1776]

Here is the Problem: For a movie scene, an 85.0 kg stunt double falls 12.0 m from a building onto a large inflated landing pad. After touching the landing pad surface, it takes her 0.477 s to come to a stop. What is the magnitude of the average net force on her as the landing pad stops her?

IS THIS CORRECT, wheres the mistake?

First, find the speed of the stunt woman as she hits the landing pad:

v² = v₀² + 2gΔy
= 0 + 2(-9.80m/s²)(-12.0m)
v = 15.3m/s

Now, the rate of acceleration required to bring her to a stop is:

a = Δv / Δt
= (v - v₀) / t
= (0 - 15.3m/s) / 0.477s
= -32.1m/s²

So, the force that stops her is:

F = ma
= 85.0kg(-32.1m/s²)
= -2.73kN (-2730N rounded)

You could also use the impulse momentum theorem:

FΔt = Δp
F = Δp / Δt
= [mv(f) - mv(i)] / t
= m[v(f) - v(i)] / t
= 85.0kg(0 - 15.3m/s) / 0.477s
= -2730N (rounded)

Please give a through answer

 

[berkeman]

Here is the Problem: For a movie scene, an 85.0 kg stunt double falls 12.0 m from a building onto a large inflated landing pad. After touching the landing pad surface, it takes her 0.477 s to come to a stop. What is the magnitude of the average net force on her as the landing pad stops her?

IS THIS CORRECT, wheres the mistake?

First, find the speed of the stunt woman as she hits the landing pad:

v² = v₀² + 2gΔy
= 0 + 2(-9.80m/s²)(-12.0m)
v = 15.3m/s

Now, the rate of acceleration required to bring her to a stop is:

a = Δv / Δt
= (v - v₀) / t
= (0 - 15.3m/s) / 0.477s
= -32.1m/s²

So, the force that stops her is:

F = ma
= 85.0kg(-32.1m/s²)
= -2.73kN (-2730N rounded)

You could also use the impulse momentum theorem:

FΔt = Δp
F = Δp / Δt
= [mv(f) - mv(i)] / t
= m[v(f) - v(i)] / t
= 85.0kg(0 - 15.3m/s) / 0.477s
= -2730N (rounded)

Please give a through answer

Your first method looks okay to me (didn't check the 2nd). I would call the force positive, though, since it's pointing up to decelerate her...

 

[tomcue]

.

Your calculations and use of equations seem to be correct. However, there are a few minor mistakes that could have been made while inputting the values into the calculator or rounding off the final answer. It is always important to double check your calculations and make sure that the units are consistent throughout. Additionally, the negative sign in the final answer indicates that the force is acting in the opposite direction of the motion, which could be misinterpreted if not properly stated. Overall, your approach to solving the problem is correct and there are no major mistakes. Great job!