Final answer:
The force of friction when two boys push a box to the right with forces of 3N and 6N and a net force of 7N is calculated to be 2 newtons.
Step-by-step explanation:
The question pertains to calculating the force of friction when two boys are pushing a box on a rough surface with forces of 3N and 6N to the right, and the net force is given as 7N.
To find the force of friction, we need to use the concept of net force from Newton's second law of motion.
The net force is the sum of all forces acting on the object, which in this case includes the forces the boys apply and the frictional force that opposes the motion.
Since the forces applied by the boys are both to the right and the net force is also to the right (since the box is still moving to the right), the force of friction must be acting to the left.
The net force (7N) is less than the total force applied by the boys (3N + 6N = 9N) because of the opposing force of friction. So, the force of friction can be found by subtracting the net force from the total force applied.
Force of friction = Total force applied by the boys - Net force
Force of friction = 9N - 7N
Force of friction = 2N
Therefore, the force of friction is 2 newtons.