In a crash test the strapped-in,75-kg dummy moves a distance of 0.80 m when the test car is slammed straight into a wall at 11.2 m/s (~25 mph).The average force acting on the dummy during the collision is how many times his own weight?
A)0.13
B)78
C)0.71
D)8.0
E)4.0

Question

Quizplus · Accepted Answer

We can use the equation F = ma, where F is the force, m is the mass of the dummy (75 kg), and a is the acceleration. The distance can be used to find the time of impact using the formula: 
d = ½ at² 
0.80 m = ½ a (11.2 m/s)
a = 2(0.80 m)/(11.2 s)² = 0.0331 m/s²
Therefore, the force acting on the dummy is:
F = ma = (75 kg)(0.0331 m/s²) = 2.48 N
To find how many times his own weight is being exerted, we divide the force by the weight (mg):
F/(mg) = 2.48 N/(75 kg x 9.81 m/s²) = 0.032
Thus, the answer is closest to 8.0, which is choice D.

In a Crash Test the Strapped-In,75-Kg Dummy Moves a Distance