Multiple physics questions including: forces on a lifted bowling ball, forces on a falling brick, free-body diagram of a suitcase on a luggage cart, and a free-body diagram of a to... Multiple physics questions including: forces on a lifted bowling ball, forces on a falling brick, free-body diagram of a suitcase on a luggage cart, and a free-body diagram of a tossed ball in the air.

Understand the Problem

The image contains multiple physics questions regarding forces and free-body diagrams. Question 28 asks about forces on a lifted bowling ball. Question 29 concerns forces acting on a falling brick. Question 30 requires a free-body diagram of a suitcase on a luggage cart. Finally, Question 31 is a challenge to draw a free-body diagram of a tossed ball in the air.

Answer

**Question 28** Forces on the ball: $F_{hand}$, $F_g = mg$. Forces exerted by the ball: $F'_{hand}$, $F'_g$. Objects forces are exerted on: Hand, Earth. **Question 29** Force on the brick: $F_g = mg$. Force exerted by the brick: $F'_g$. Object force is exerted on: Earth. **Question 30** Suitcase: $F_{g,suitcase} = m_{suitcase}g$, $F_{N,suitcase}$. Luggage Cart: $F_{g,cart} = m_{cart}g$, $F'_{N,suitcase}$, $F_{N,ground}$. Interaction Pairs: $F_{N,suitcase}$ and $F'_{N,suitcase}$, $F_{g,suitcase}$ and $F'_{g,suitcase}$, $F_{N,ground}$ and the normal force of cart on the ground, $F_{g,cart}$ and $F'_{g,cart}$. **Question 31** Force on the ball: $F_g = mg$. Force exerted by the ball: $F'_g$. Object force is exerted on: Earth.

Steps to Solve

Question 28

Identify forces acting on the bowling ball

Since you are lifting the ball upward, there are two main forces acting on it:

The upward force, $F_{hand}$, exerted by your hand.
The downward force of gravity, $F_g$, which can also be written as $mg$, where $m$ is the mass of the ball and $g$ is the acceleration due to gravity (approximately $9.8 m/s^2$).

Identify forces exerted by the bowling ball

According to Newton's third law, for every action there is an equal and opposite reaction. The bowling ball exerts the following:

A downward force on your hand, $F'_{hand}$, which is equal in magnitude and opposite in direction to the force your hand exerts on the ball.
An upward gravitational force on the Earth, $F'_g$, which is equal in magnitude and opposite in direction to the gravitational force exerted by the Earth on the ball.

Identify the objects on which these forces are exerted

The downward force exerted by the ball is exerted on your hand.
The upward gravitational force exerted by the ball is exerted on Earth.

Question 29

Identify forces acting on the brick

As the brick falls, and since air resistance is ignored, the only force acting on the brick is the force of gravity, $F_g = mg$, pulling it downward.

Identify forces exerted by the brick

The brick exerts an upward gravitational force on the Earth, $F'_g$, equal in magnitude and opposite in direction to the force of gravity exerted by the Earth on the brick.

Identify the object on which this force is exerted

The upward gravitational force exerted by the brick is exerted on the Earth.

Question 30

Draw free-body diagram for the suitcase

The suitcase experiences two forces:

The downward force of gravity, $F_{g,suitcase} = m_{suitcase}g$, where $m_{suitcase}$ is the mass of the suitcase.
The upward normal force, $F_{N,suitcase}$, exerted by the cart on the suitcase, which balances the gravitational force since the suitcase is stationary.

Draw free-body diagram for the luggage cart

The luggage cart experiences multiple forces:

The downward force of gravity, $F_{g,cart} = m_{cart}g$, where $m_{cart}$ is the mass of the cart.
The downward normal force, $F'{N,suitcase}$, caused by the suitcase sitting on the cart. This is the reaction force to the normal force exerted by the cart on the suitcase. According to Newton's 3rd law, it's equal in magnitude to the normal force $F{N,suitcase}$.
The upward normal force from the ground, $F_{N,ground}$, which balances the total downward force ($F_{g,cart}$ and $F'_{N,suitcase}$).

Identify interaction pairs

There are two interaction pairs:

The normal force of the cart on the suitcase, $F_{N,suitcase}$, and the normal force of the suitcase on the cart, $F'_{N,suitcase}$.
The gravitational force of the Earth on the suitcase, $F_{g,suitcase}$, and the gravitational force of the suitcase on the Earth, $F'_{g,suitcase}$. Similarly, the gravitational force of the Earth on the cart and the gravitational force of the cart on the Earth.
The normal force of the ground on the cart, $F_{N,ground}$, and the normal force of the cart on the ground (a force not included in the free body diagram).

Question 31

Draw free-body diagram for the ball

Since air resistance is negligible, the only force acting on the ball after it leaves your hand is the downward force of gravity, $F_g = mg$, where $m$ is the mass of the ball and $g$ is the acceleration due to gravity. Note that the ball is still moving upward, but the net force is downwards, causing it to decelerate as it rises.

Identify forces exerted by the ball

The ball exerts an upward gravitational force on the Earth, $F'_g$, equal in magnitude and opposite in direction to the force of gravity exerted by the Earth on the ball.

Identify the object on which this force is exerted

The upward gravitational force exerted by the ball is exerted on the Earth.

Question 28

Forces on the ball:

Upward force by hand: $F_{hand}$
Downward force of gravity: $F_g = mg$

Forces exerted by the ball:

Downward force on hand: $F'_{hand}$
Upward (small) gravitational force on Earth: $F'_g$

Objects forces are exerted on:

Hand
Earth

Question 29

Forces on the brick:

Downward force of gravity: $F_g = mg$

Forces exerted by the brick:

Upward (small) gravitational force on Earth: $F'_g$

Objects forces are exerted on:

Earth

Question 30

Suitcase:

Downward gravity: $F_{g,suitcase} = m_{suitcase}g$
Upward normal force from cart: $F_{N,suitcase}$

Luggage Cart:

Downward gravity: $F_{g,cart} = m_{cart}g$
Downward normal force from suitcase: $F'_{N,suitcase}$
Upward normal force from ground: $F_{N,ground}$

Interaction Pairs:

$F_{N,suitcase}$ and $F'_{N,suitcase}$
$F_{g,suitcase}$ and $F'_{g,suitcase}$
$F_{N,ground}$ and the normal force of the cart on the ground.
$F_{g,cart}$ and $F'_{g,cart}$

Question 31

Forces on the ball:

Downward gravity: $F_g = mg$

Forces exerted by the ball:

Upward (small) gravitational force on Earth: $F'_g$

Objects forces are exerted on:

Earth

More Information

These problems are a good review of Newton's Laws, specifically the 2nd Law ($\sum F = ma$) and 3rd Law (action/reaction pairs). Free-body diagrams are essential tools for visualizing and analyzing the forces acting on an object.

Tips

Ignoring forces: Forgetting to include gravity is a common mistake, especially on Earth.
Incorrect direction: Drawing forces in the wrong direction (e.g., gravity pointing upward).
Confusing forces acting on an object with forces exerted by the object: Newton's 3rd Law is often misunderstood. Remember to distinguish between the forces acting on an object and the forces the object exerts.
Including forces that don't exist: In Question 31, many students include an upward force after the ball leaves the hand, even though the hand is no longer in contact with the ball. Once the ball leaves the hand, the only force acting on the ball (neglecting air resistance) is gravity.
Mixing up mass and weight: Mass is a scalar and weight is a force. Weight is the product of mass and the acceleration due to gravity ($W=mg$).

AI-generated content may contain errors. Please verify critical information

Thank you for voting!

Understand the Problem

Answer

Answer for screen readers

Steps to Solve

More Information

Tips