1- The forces are said to be in equilibrium if: (a) F=0 (b) acceleration =0 (c) velocity remains constant (d) all (a), (b) and (c) 2- The mathematical form of Newton's first law is: (a) F=ma (b) F=0 (c) F12=F21 3- The mathematical form of Newton's third law is: (a) F=ma (b) F=0 (c) F12=F21 4- The mathematical form of Newton's second law is: (a) F=ma (b) F=0 (c) F12=F21 5- Newton's first law sometimes called: (a) law of momentum (b) law of inertia (c) law of force 6- The force that the Earth exerts on an object is called: (a) friction force (b) gravitational force (c) tensile force 7- The gravitational force acts on an object is called: (a) weight (b) acceleration (c) average speed 8- The unit of weight is: (a) Newton (b) Joule (c) Pascal 9- An object at rest, remains at rest and an object in motion, continues in motion with a constant velocity, if the net force acting on it is: (a) parallel (b) equal (c) zero Write the scientific concept for the followings: 1- It causes an object to accelerate 2- The net force exerted on an object is zero 3- When no force acts on an object, the acceleration is zero