Chapter 4 Questions
1. If the acceleration of an object is zero, are no forces acting on it? Explain.
a. No, forces would still be acting on an object if its acceleration is zero. Acceleration is only the change in velocity and in the F=ma equation, the F stands for net force. For example, if a car was traveling at a constant velocity, it would still have forces such as gravity, friction, and normal force acting on it.
2. Only one force acts on an object. Can the object have zero acceleration? Can it have zero velocity? Explain.
a. If only one force acts on the object, then the net force cannot be zero. Therefore, it cannot have zero acceleration. The object can have zero velocity for an instant. For example, an object thrown straight up …show more content…
When a golf ball is dropped to the pavement, it bounces back up. (a) Is a force needed to make it bounce back up? (b) If so, what exerts the force? (c) Is this force greater or less than when the ball is sitting on the pavement? Why? (draw a free body diagram)
a. Yes, there must be a force on the golf ball to make it accelerate upward.
b. The normal force on the pavement exerts the force.
c. This force is greater than when the ball is sitting on the pavement. The force required to keep the ball on the pavement is equal and opposite to gravity. The force that makes the ball bounce upwards has to counteract the force that the ball gained while it was being dropped. (see drawings page)
4. Why might your foot hurt if you kick a heavy desk or wall?
a. When you kick a heavy desk or wall, your foot exerts a force on the desk or wall. The desk or wall exerts an equal force on your foot.
5. Suppose that you are standing on a cardboard carton that just barely supports you. What you happen to it if you jumped up into the air? It would (a) collapse; (b) be unaffected; (c) spring upward a bit; (d) move …show more content…
You are trying to push your stalled car. Although you apply a horizontal force of 400 N to the car, it doesn’t budge, and neither do you. Which force(s) must also have a magnitude of 400N: (a) the force exerted by the car on you; (b) the friction force exerted by the car on the road; (c) the normal force exerted by the road on you; (d) the friction force exerted by the road on you?
a. The forces in (a), (b), and (d) are all equal to 400 N. (a) You exert a force of 400 N on the car. Because of Newton’s third law, the force of the car on you is 400 N.
b. (b) Since the car doesn't move, the friction force exerted by the road on the car must equal 400 N, too. Therefore, the friction force is also 400 N.
c. (c) The normal force exerted by the road on you will be equal and opposite to the gravity acting on you. Therefore, it doesn’t have to be 400 N.
d. (d) The car is exerting a 400 N force on you, and because you are not accelerating, the ground exerts an equal and opposite horizontal force. Therefore, the friction force of the road on you is 400 N.
5. Suppose two forces act on an object, one fore proportion to v and the other proportion to v2. Which force dominates at high speed?
a. The force proportional to v2 will dominate at high
1. If the acceleration of an object is zero, are no forces acting on it? Explain.
a. No, forces would still be acting on an object if its acceleration is zero. Acceleration is only the change in velocity and in the F=ma equation, the F stands for net force. For example, if a car was traveling at a constant velocity, it would still have forces such as gravity, friction, and normal force acting on it.
2. Only one force acts on an object. Can the object have zero acceleration? Can it have zero velocity? Explain.
a. If only one force acts on the object, then the net force cannot be zero. Therefore, it cannot have zero acceleration. The object can have zero velocity for an instant. For example, an object thrown straight up …show more content…
When a golf ball is dropped to the pavement, it bounces back up. (a) Is a force needed to make it bounce back up? (b) If so, what exerts the force? (c) Is this force greater or less than when the ball is sitting on the pavement? Why? (draw a free body diagram)
a. Yes, there must be a force on the golf ball to make it accelerate upward.
b. The normal force on the pavement exerts the force.
c. This force is greater than when the ball is sitting on the pavement. The force required to keep the ball on the pavement is equal and opposite to gravity. The force that makes the ball bounce upwards has to counteract the force that the ball gained while it was being dropped. (see drawings page)
4. Why might your foot hurt if you kick a heavy desk or wall?
a. When you kick a heavy desk or wall, your foot exerts a force on the desk or wall. The desk or wall exerts an equal force on your foot.
5. Suppose that you are standing on a cardboard carton that just barely supports you. What you happen to it if you jumped up into the air? It would (a) collapse; (b) be unaffected; (c) spring upward a bit; (d) move …show more content…
You are trying to push your stalled car. Although you apply a horizontal force of 400 N to the car, it doesn’t budge, and neither do you. Which force(s) must also have a magnitude of 400N: (a) the force exerted by the car on you; (b) the friction force exerted by the car on the road; (c) the normal force exerted by the road on you; (d) the friction force exerted by the road on you?
a. The forces in (a), (b), and (d) are all equal to 400 N. (a) You exert a force of 400 N on the car. Because of Newton’s third law, the force of the car on you is 400 N.
b. (b) Since the car doesn't move, the friction force exerted by the road on the car must equal 400 N, too. Therefore, the friction force is also 400 N.
c. (c) The normal force exerted by the road on you will be equal and opposite to the gravity acting on you. Therefore, it doesn’t have to be 400 N.
d. (d) The car is exerting a 400 N force on you, and because you are not accelerating, the ground exerts an equal and opposite horizontal force. Therefore, the friction force of the road on you is 400 N.
5. Suppose two forces act on an object, one fore proportion to v and the other proportion to v2. Which force dominates at high speed?
a. The force proportional to v2 will dominate at high