Answer:
a
   
b
   
Explanation:
From the question we are told that 
           The mass of the rock is  
           The  length of the small object from the rock is  
           The  length of the small object from the branch 
An image representing this lever set-up is shown on the first uploaded image 
Here the small object acts as a fulcrum 
The  force exerted by the weight of the rock is mathematically evaluated as
       
substituting values 
      
      
  So  at  equilibrium the sum  of the moment about the fulcrum is mathematically represented as 
          
Here   is very small so
 is very small so   
 
                                and  
Hence 
        
=>    
substituting values 
         
        
The  mechanical advantage is mathematically evaluated as 
           
substituting values 
         
        
 
        
             
        
        
        
To answer these questions just use the equations for potential energy using the mass and heights described. the potential energy at the prescribed heights = the initial kinetic energy required to reach that height.
Make sure you calculate the force of gravity on the surface using the radius of the planet.
        
             
        
        
        
Answer:
sum of all forces on the air plane must be ZERO
So both forces must be of same magnitude
Explanation:
As we know that airplane is moving with uniform speed is horizontal plane is a straight line
so the motion of the air plane is uniform without any acceleration
So we will have

acceleration must be zero
now by Newton's law


so sum of all forces on the air plane must be ZERO
 
        
             
        
        
        
Answer: here are 1,000m in a km, so 200km is 200,000m
200,000m/10m/s = 20,000s
Explanation:
 
        
                    
             
        
        
        
1. The balls move to the opposite direction but the same speed. This represents Newton's third law of motion.
2. The total momentum before and after the collision stays constant or is conserved.
3. If the masses were the same, the velocities of both balls after the collision would exchange.
4 and 5. Use momentum balance to solve for the final velocities.