It has a constant acceleration of 16.4 m/s2 for the first 1.50 s. then its fuel is exhausted, and it is in free fall. the rocket has a mass of 78.2 g; the mass of the fuel is much less than 78.2 g. ignore air resistance. what was the downward net force on the rocket after its fuel was spent?

The force downward acting o the rocket is F=m*g=0.0782kg*9.8m/s^2=0.76636 N

Explanation:

Since the fuel of the rocket was spent and we are ignoring the air resistance, so the rocket is a free fall movement, which means that the only force acting on him is the weight, now the equation for the weight is:

where m is the mass of the object that is falling and g is the gravitational acceleration, which in the earth is nearly 9.8m/s^2.

now here i have to do the observation that the mass of the rocket might be wrong because it says 78.2 grams and a rocket has a lot more mass than that, but whatever is the mass of the rocket the procedure to calculate the force is the same (since the fuel has been spent).

we have to convert the mass to Kg so the force will be in Newtons:

and now we just use the equation for the weight:

now again here i do the observation that the weight of a rocket should be a lot more than this but the procedure to calculate is the same.

the chart show the masses and velocities of two colliding objects that stick together after a collision.

according to the law of conservation of momentum, the momentum of the object after the collision is  

answer

1,500

kg • m/s.