Answer:
Fd
Explanation:
Work is force times distance. If you push on an object really hard but it does not budge, you have still performed no work on it, because anything times zero is still zero. 
 
        
                    
             
        
        
        
Answer:
Explained below
Explanation:
Newton's first law of motion: This law states that an object will remain at rest or continue in constant motion except it's acted upon by an external force. In projectile motion, the horizontal component of velocity will remain unchanged because we ignore air resistance since no force is acting in that horizontal direction.
Newton's second law of motion: This law states that force is the product of mass and acceleration. In projectile the force acts downwards, thus f = mg. 
But g = a since internal forces will cancel out.
Thus, F = ma