Posted by **johnny** on Thursday, December 11, 2008 at 8:04pm.

A 72 kg man drops to a concrete patio from a window only 0.60 m above the patio. He neglects to bend his knees on landing, taking 2.0 cm to stop.

(a) What is his average acceleration from when his feet first touch the patio to when he stops?

m/s2

(b) What is the magnitude of the average stopping force?

kN

- physics -
**bobpursley**, Thursday, December 11, 2008 at 8:11pm
I will be happy to critique your thinking.

- physics -
**Christiaan**, Thursday, December 11, 2008 at 8:14pm
a) First you calculate his speed of impact (the speed when he hits the ground).

For this you can use the formula:

v² = v0² + 2.a.x

where:

-v is your final speed

-v0 is your initial speed (0 m/s in this case)

-a is your acceleration (the gravitational acceleration in this case, being 9.81 m/s²)

-x, the distance travelled (being 0.6 m in this case)

so v² = 2*9.81 m/s²*0.6 m = 11.77 m²/s²

Now, we can use the same formula to calculate his average acceleration when he is slowing down.

v² = v0² + 2*a*x

- v being 0 m/s in this case

- v0² being 11.77 m²/s² (since he starts slowing down at this speed)

- x, being 0.02m

=> a = (v² - v0²)/(2*x) = (-11.77 m²/s²)/(2*0.02m) = - 294,25 m/s²

- physics -
**Christiaan**, Thursday, December 11, 2008 at 8:17pm
b) Since F = m*a

The average stopping force can be calculated as:

F = 72 kg* -294.25 m/s² = -21.186 kN

The negative sign for both the acceleration and stopping force means they are poiting upward, since we took the downward direction to be positive.

## Answer this Question

## Related Questions

- physics - A 72 kg man drops to a concrete patio from a window only 0.60 m above ...
- geometry - John is putting in a concrete patio in his backyard. The dimensions ...
- Math - 1. Suppose you want to buy concrete for a 36ft by 24 ft by 9 in. patio. ...
- trigonometry ASAP! - wendell is setting concrete on a triangular patio. one side...
- Math - Pouring concrete into backyard. The patio slab will be 7m long, 2m wide ...
- Math - The plan for a rectangular patio has a square garden centered in the ...
- Math - The Gilberts are designing a rectangular patio for their backyard. The ...
- Math - The Gilberts are designing a rectangular patio for their backyard. The ...
- physics - When jumping straight down, you can be seriously injured if you land ...
- Math - Area od a patio is 24 meters. sq. A patio stone is square with each side ...

More Related Questions