Peoples Physics Book Version-2

6.2. Newton’s Laws Explained http://www.ck12.org

Solution

a) Neither. Both Tom and Mary will travel the same distance. The forced applied to each person is the same
(Newton’s Third Law). So

Ma =ma

which cancels to

a=a

Therefore both people will travel the same distance because the acceleration controls how far someone will travel
and Tom and Mary have equal acceleration.

b) Mary will go farther. Again, the same force is applied to both Mary and Tom so

Ma=ma

Since Tom has the larger mass, his acceleration must be smaller (acceleration and mass are inversely proportional).
Finally, because Mary’s acceleration is greater, she will travel farther.

c) Neither. Newton’s Third Law states that for every action there is an equal and opposite reaction. Therefore if Tom
pushes twice as hard as Mary, Mary will essentially be pushing back with the same strength. They will therefore
travel the same distance.