Newton's laws (physics problems)

[nicha89]

i got some problems to explain but i coudn't, please help me if u have any idea:

1. people sitting in cars get rear-ended, frequently suffer whlisplash injuries to their necks. how does newton's 1st law explain the motion of their bodies that results in this type of injury? (hint: think separately about what is happening to their bodies and to their heads)

2. in a binary star system, companion stars swing in orbit around each other due to the gravitational forces that each start exerts on the other. they thereby constitute an action/reaction pair. you gaze thru the telescope at a different section of the sky and notice what appears to be a lone star that seems to be swinging aound in the same way as starts do in a binary system. try as you might. you cannot see its companion start.

A. what does newton's 3rd law allow you to deduce about WHAT MUST BE inthe seemingly empty space about which the lone start is circling?

B. how does newton's 3rd law allow this deduction?

thank u very much!

[Al42]

1. The head tends to stay where it is, since there's (relatively) no force acting on it. (The force that is acting on it is the force that causes the whiplash injury.) The body tends to move forward rapidly because the seat is pushing it. (Which is why headrests tend to prevent whiplash injuriy.)

2.
A. Mass. Nothing more can be deduced using only Newton's 3^rd law.
B. An exercise left for the student.