PHYS 101 Homework week 2

1. 2/2 points Two children pull on a sled in opposite directions, each pulling with a force of 27 N. What is the approximate net force acting on the sled? The net force acting on the sled is zero because the forces balance each other. Correct. (Since the children pull with equal forces in opposite directions, the net force is zero. If one child pulled with more force than the other, there would be a net force in the direction of the greater force. ) 2. 2/2 points Two children pull on a sled, one to the left with a force of 22 N and the other to the right with a force of 30 N. Consider the force of friction small enough to ignore. What is the net force acting on the sled? The net force is 8 N to the right, since the force to the right is larger in magnitude than the force to the left (Correct. The net force is found by adding all forces acting on an object together while keeping direction in mind. In this case the force to the left balances 22 N of the force to the right, so that the remaining force to the right, 8 N, is the net force. ) 3. 2/2 points A book is accidentally left on the roof of a car as the driver drives away. As the car and the book move with constant velocity along the street, what must be true about the magnitude (size) of the forces acting on the book? Choose the best answer. Static friction between the book and the roof of the car has the same magnitude as kinetic friction caused by air resistance. (Correct. Since the book is not accelerating, the net force acting on the book must be zero. The forces are balanced. ) 4. 2/2 points A calculator is set on top of a book and the book is then pushed so that it slowly accelerates across a desk, taking the calculator with it. The person pushing the book does not touch the calculator. What type of force causes the calculator to accelerate? The calculator is accelerated by a static friction force caused by the book. (Correct. This is because the calculator is touching the book (not the person's hand) and because the calculator is not moving (static) with respect to the top of the book.) 5. 2/2 points Two football players collide during a game. Player A weighs considerably more than player B and therefore must have more mass than player B. When the players collide, which player exerts a larger force on the other? . Both players apply the same size force to each other (forces of the same magnitude.)