Answer:
Work = power * time
time = 20000 joules / 1000 joules / sec = 20 sec
Answer:

Acceleration, in m/s, of such a rock fragment = 
Explanation:
According to Newton's Third Equation of motion

Where:
is the final velocity
is the initial velocity
a is the acceleration
s is the distance
In our case:

So Equation will become:

Acceleration, in m/s, of such a rock fragment = 
Answer:
150000000000 m
0.0000005 seconds
33.33 ns
Explanation:
Speed of electromagnetic waves through vacuum = 
Echo time = 1000 seconds
Echo time is the time taken to reach the object and come back to the observer
Distance = Speed×Time

Venus is 150000000000 m away from Earth
Time = Distance / Speed

Echo time will be twice the time

The echo time will be 0.0000005 seconds
Difference in time = Difference in distance / Speed

The accuracy by which I will be able to measure the echo time is 33.33 ns
Force = (mass) x (acceleration) (Newton's second law of motion)
Divide both sides of the equation by 'acceleration', and you have
Mass = (force) / (acceleration)
Mass = 17 newtons / 3.75 meters per second-sqrd = 4.533 kilograms (rounded)
<span>This is best understood with Newtons Third Law of Motion: for every action there is an equal and opposite reaction. That should allow you to see the answer.</span>