Answer:

Explanation:
Since the system is in international space station
so here we can say that net force on the system is zero here
so Force by the astronaut on the space station = Force due to space station on boy
so here we know that
mass of boy = 70 kg
acceleration of boy = 
now we know that


now for the space station will be same as above force




Answer:
0°
Explanation:
The angle between force and displacement should be 0° in order to get the maximum work done.
Work done = Force x dcosФ°
Ф is the angle between force and displacement
When Ф is zero, the maximum work done is attained
When Ф is 90, the minimum work is done, in fact, work done is 0
Answer:
Acceleration will be 
Explanation:
We have given initial speed of the car is 70 km/hr
We know that 1 km = 1000 m
And 1 hour = 3600 sec
So 
It is given that car stops in 12 sec
So final speed of the car v = 0 m/sec
Time t = 12 sec
From first equation of motion v = u+at
So 
( negative sign indicates that speed of the car will constantly decrease )
By adding a vibration at the natural frequency of the medium-A
Solid particles hope this helped!