physics 問題 20分

(a) Fnet = ma
= (1)(1)
= 1N

(b) Fnet acting on A = - Fnet acting on B
= - 1 N

(c) a = (v-u)/ t
1 = v / 0.5
v = 0.5ms^-1
(m1)(u1) + (m2)(u2) = (m1)(v1) + (m2)(v2)
(3)(3) + (1)(0) = (3)(v) + (1)(0.5)
9 + 0 = 3v + 0.5
v = 17 / 6ms-1 ( 2.83 )


i have that book also, the ans. for (c) should be 2.83

As carA impacts carB, carAs (3kgm/s) momentum approaches 0 according to Newton's Law of Conservation of Momentum. (what I learned ages ago)

3X3+1X0=1Xvelocity of carB

CarB would have a velocity of 9m/s theoretically assuming no thermal and
other sound energy loss... . Since F=ma. During collision, the kinetic energy
is shifted from A to B. It takes an differential equation to show the
transitional shift of this energy from A to B with respect to time as the
integral parameters. To this point, I can only say car A will come to a dead
stop after impact.

These toy cars are pretty heavy for toys don't you think???