Chapter 6, Problem 10P

### College Physics

11th Edition
Raymond A. Serway + 1 other
ISBN: 9781305952300

Chapter
Section

### College Physics

11th Edition
Raymond A. Serway + 1 other
ISBN: 9781305952300
Textbook Problem

# A man claims he ran safely hold on to a 12.0-kg child in a head-on collision with a relative speed of 120-mi/h lasting for 0.10 s as long as he has his seat belt on. (a) Find the magnitude of the average force needed to hold onto the child, (b) Based on the result to part (a), is the man’s claim valid? (c) What does the answer to this problem say about laws requiring the use of proper safely devices such as seat belts and special toddler seats?

(a)

To determine
The magnitude of the average force.

Explanation

Given Info: The mass of a child is 12.0â€‰kg , initial velocity of the man is 120â€‰mi/h , and time taken by the man holds the child is 0.10â€‰s .

The expression for impulse is,

I=FavÎ”t

• Fav is the average force
• I is the impulse
• Î”t is the duration of time

Rewrite the expression for average force with magnitude

|Fav|=|I|Î”t

The impulse of the man must deliver to the child is,

|I|=mchild|vfâˆ’vi|Î”t

• mchild is the mass of the child
• vf is the final velocity
• vi is the initial velocity

Substitute 12.0â€‰kg for m, 0 for vf , 120â€‰mi/h for vi and 0

(b)

To determine
Man’s claim with child is valid or invalid.

(c)

To determine
The required laws used for safety devices.

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