A spacecraft in outer space increases velocity by firing its rockets. How can hot gases escaping from its rockets change the velocity of the craft when there is nothing in space for the gases to push against?

Momentum is conserved.

Explanation:

-Momentum is conserved.

-By Newton's third law (For every action, there is an equal and opposite reaction.)-the change in momentum of gases in one direction must be balanced by an equal change in momentum of the spacecraft in the opposite direction.

speed of object after 2 seconds will be 6 ms⁻¹

Explanation:

Initial velocity = 0

Final Velocity = 21 m/s

Time = 7 sec

We need to find speed of object after 2.0 seconds.

First we will find acceleration using formula:

Putting values:

Now finding speed of object after 2 seconds

The formula used will be:

Putting values of a= 3m/s², t=2 sec and v₀=0 (at rest)

So, speed of object after 2 seconds will be 6 ms⁻¹