Newtons Laws of Motion - Homeschooling Exercises - Free Printable

Here are the step-by-step solutions for the problems on the worksheet.

1. Net Force Calculation
* Reasoning: When two people push an object in the same direction, their forces add together.
* Chris's force: $50 \text{ lbf}$
* Julia's force: $30 \text{ lbf}$
* Total Force = $50 + 30 = 80 \text{ lbf}$.
* Answer: a. 80 lbf

2. Net Force on a Standing Man
* Reasoning: The man is standing still (he is not moving up, down, left, or right). In physics, if an object is not accelerating, the net force acting on it is zero. Gravity pulls him down, but the ground pushes him up with equal force, canceling each other out.
* Answer: c. 0 lbf

3. Water Drops and Tangential Motion
* Reasoning: While the water is on the wheel, it moves in a circle because a force pulls it inward. Once it leaves the wheel, that pulling force stops. According to Newton's First Law (Inertia), the water wants to keep moving in a straight line at the speed it had at that exact moment. This straight-line path off a curve is called "tangential." This tendency to keep moving is due to inertia.
* Answer: b. Inertia

4. Coin and Cardboard Trick
* Reasoning: This is a classic inertia demonstration. The coin has mass, so it has inertia (it wants to stay at rest). When you pull the cardboard *swiftly*, the friction between the card and the coin isn't strong enough or fast enough to overcome the coin's inertia. The card shoots out, but the coin stays in place horizontally and drops straight down into the glass.
* Answer: c. The coin will fall into the glass

5. Comparing Inertia (Feather, Ball, Plate)
* Reasoning: Inertia is directly related to mass. The more mass an object has, the more inertia it has (the harder it is to start or stop moving). The problem states they all have the same mass. Therefore, they all have the same amount of inertia.
* Answer: d. All will have the same inertia

6. Baseballs with Different Masses
* Reasoning: Since inertia depends on mass, the object with the greater mass has the greater inertia. Chris's ball is heavier than Steve's ball. Therefore, Chris's ball has more inertia.
* Answer: c. Chris's ball

7. People Moving Backward in a Bus
* Reasoning: Before the bus moves, the people inside are at rest. Their bodies have inertia, meaning they want to *stay* at rest. When the bus accelerates forward, the floor moves under their feet, but their upper bodies try to stay in the original position. This feels like being pushed backward, but it is actually just their inertia resisting the change in motion.
* Answer: c. Inertia due to rest

8. Conservation Law (No External Force)
* Reasoning: Newton's Second Law relates force to acceleration ($F=ma$). If there is no external force ($F=0$), there is no acceleration. If there is no acceleration, the velocity does not change. In physics, the quantity defined as mass times velocity is momentum. Therefore, without external forces, momentum is conserved.
* Answer: Momentum

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Final Answer:
1. a
2. c
3. b
4. c
5. d
6. c
7. c
8. Momentum