R = (2+2+1) i - (t+1)] + t3 k
what is the direction of initial velocity

In the - j direction, that is negative of the y-axis

Explanation:

As typed in the question, the position of the object is given by the expression in three component ( i, j, k) form:

r (t) = 5  i  - (t + 1 )  j  + t^3  k

and since the velocity is the derivative of position with respect to time, by doing the derivative of this expression we get:

v(t) = 0  i  -  1  j   +3 t^2  k

which for the initial velocity requested (that is at time zero) we have:

v(t) = 0  i  -  1  j   +3 (0)^2  k = = 1  j

Then the direction of the initial velocity is entirely in the direction of the j versor, that is pointing to the negative of the y-axis.

explanation:

newton's third law, for every action there is an equal and opposite reaction.

can be answered using momentum.

momentum = p

p1= mass1 * velocity1

p1 = p2

therefore

p1 = 6kg * 4m/s

p1 = 24kgm/s

p2=m2 * v2

24 kgm/s = 7kg * v2

v2 = 24 kgm/s / 7kg

v2= 3.42 m/s