Answer:
a)5.925
ii)149.5 or383.5
Explanation:
ii)3.9×105-2.5×104
 409.5-260
the zero in 260 may or may not be significant since it is after two significant figures thus we have two options
 
        
             
        
        
        
Answer:
Planet will crash on to the Sun if the tangential velocity becomes zero and Rocket should be fired  from Earth's orbit is at 30 m/s and in opposite direction to the Earth orbits the Sun
Explanation:
The orbital velocity of the Earth about the sun is 30 km/s. If we shoot a rocket with 30 km/s with respect to Earth in the opposite direction.  Then the two velocity vectors cancel. The resultant velocity would be zero with respect to the Sun. resulting velocity is called as tangential velocity. 
Planet will crash on to the Sun if the tangential velocity becomes zero and Rocket should be fired  from Earth's orbit is at 30 m/s and in opposite direction to the Earth orbits the Sun
 
        
             
        
        
        
I would say friction because it requires to surfaces in order for the force to take place
correct me if I'm wrong.
 
        
                    
             
        
        
        
Answer:
9.8 Newton 
Explanation:
At average gravity on earth (conventionally, g=9.80665m/s2),
a kilogram mass exerts a force of about 9.8 newton
I hope this answer helps you