a man claims that he can hold onto a 12 kg child in a head on collision as long

Question

a man claims that he can hold onto a 12 kg child in a head on collision as long as he has hit seat belt on . consider this man in a collision in which he is in in one of two identical cars each traveling toward the other 60 mi/ h relative to the ground. the car in which he rides is brought to rest after 0.10 seconds. Find a- the magnitude of the average force needed to hold onto the child? b- based on the result in part a, is the man's claim valid? c- what does the answer to this problem say about laws requiring the use of proper safety devices such as seat belts and special toddler seats?

Explanation / Answer

m=12 kg

v=60 mi/hr => 26.82 m/s

1 mile is 1609.344 meters.
1 hour is 3600 seconds.

pi(momentum)= m*v=321.84 (kg*m/s)

p = Favg*t= (pf-pi)=Favg*t

pf=0 since it is brought to rest

Thus F= -pi / t = -321.84/0.1

a)F=-3218.4 N   The question asks for the magnitude so ignore the sign F=3218.4N

b)3218.4N is like being able to lift a 330kg(726 lb weight) mass from rest. No his claim is not valid

c)Buckle up, its the law! Plus its plain common sence.

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