Question

practice problems
work each of the following problems. show all work.

1. a box is being pulled across a horizontal surface by a 20 n force to the right.

a. if the box moves at a constant velocity, what do you know about the forces acting on the object?
b. if the box moves at a constant velocity, how much force opposes the motion of the box?
c. if the box experiences a force of 15 n to the left, along with the 20 n force acting to the right, what is the net force on the box?

1. a baseball bat can apply a force upwards of 18,000 n on a ball. how much force does the ball apply on the bat?
2. when you push a box with 20 n of force, what force does the box apply back on you?
3. a book that weighs 5 n sits on a table. what force does the table apply to the book?

Explanation:

Step1: Analyze constant - velocity situation

When an object moves at a constant velocity, the net force acting on it is zero according to Newton's first law.

Step2: Determine opposing force for constant - velocity box

Since the net force is zero and there is a 20 N force to the right, the force opposing the motion (friction) must be 20 N to the left so that \(F_{net}=F_{right}-F_{left}=20 - 20=0\).

Step3: Calculate net force with two forces

Given a 20 N force to the right and a 15 N force to the left, the net force \(F_{net}=F_{right}-F_{left}=20 - 15 = 5\) N to the right.

Step4: Apply Newton's third - law for bat and ball

According to Newton's third law, for every action, there is an equal and opposite reaction. So if the bat applies a 18000 N force on the ball, the ball applies a 18000 N force on the bat in the opposite direction.

Step5: Apply Newton's third - law for pushing box

If you push a box with 20 N of force, the box applies a 20 N force back on you in the opposite direction according to Newton's third law.

Step6: Apply Newton's third - law for book on table

The book weighs 5 N (downward force due to gravity). The table applies a normal force on the book. According to Newton's third - law, the table applies a 5 N force upwards on the book to balance the weight of the book.

Answer:

a. The net force acting on the object is zero.
b. 20 N
c. 5 N to the right

1. 18000 N
2. 20 N
3. 5 N