Chapter 8: Statics and Torque - Review Questions

What is the first condition necessary to achieve equilibrium?

a) The net external force on the system must be zero.

b) The net external torque on the system must be zero.

c) The system must be at rest.

d) The system must be moving at constant velocity.

a) The net external force on the system must be zero.

In which type of equilibrium is an object motionless?

a) Static equilibrium

b) Dynamic equilibrium

c) Rotational equilibrium

d) Translational equilibrium

a) Static equilibrium

What does it mean if net F_x = 0 and net F_y = 0 for a system?

a) The system is in equilibrium in both x and y directions.

b) The system is accelerating in both x and y directions.

c) The system is rotating.

d) The system is at rest.

a) The system is in equilibrium in both x and y directions.

The first condition for equilibrium states that the net external force must be ___.

zero

In static equilibrium, an object is ___.

motionless

What is the second condition necessary to achieve equilibrium in a system?

a) The net external force must be zero.

b) The net external torque must be zero.

c) The system must have constant linear velocity.

d) The system must have constant angular acceleration.

b) The net external torque must be zero.

Which of the following factors does NOT affect torque?

a) Magnitude of the force

b) Distance from the pivot point

c) Angle between force and lever arm

d) Mass of the object

d) Mass of the object

In which direction is torque considered positive by convention?

a) Clockwise

b) Counterclockwise

c) Upward

d) Downward

b) Counterclockwise

Torque is defined as the rotational equivalent of a ___.

force

The formula for torque is given by τ = rF sin θ, where r is the distance from the pivot, F is the force, and θ is the ___.

angle

The SI unit of torque is ___.

N·m

Explain why the choice of pivot point is important when calculating torque.

The choice of pivot point is important because the torque value depends on the distance from the pivot point to the point where the force is applied. Different pivot points can result in different torque values for the same force.

Describe the role of torque in rotational mechanics.

Torque is crucial in rotational mechanics as it determines the effectiveness of a force in causing rotational acceleration. It plays a similar role in rotational motion as force does in linear motion.

What is the characteristic of a system in stable equilibrium?

a) It experiences a net force in the direction of displacement.

b) It experiences a net force opposite to the direction of displacement.

c) Its equilibrium is independent of displacement.

d) It accelerates away from equilibrium when displaced.

b) It experiences a net force opposite to the direction of displacement.

Which of the following is an example of neutral equilibrium?

a) A marble at the bottom of a bowl

b) A ball on top of a hill

c) A marble on a flat horizontal surface

d) A pencil standing on its tip

c) A marble on a flat horizontal surface

Why is a chicken considered to be in very stable equilibrium?

a) Its center of gravity is above its hip joints.

b) Its center of gravity is below its hip joints and above a broad base of support.

c) It has a narrow base of support.

d) Its center of gravity is above its head.

b) Its center of gravity is below its hip joints and above a broad base of support.

A system is in ___ equilibrium if it experiences a net force or torque in the same direction as the displacement from equilibrium.

unstable

The center of gravity of a chicken lies below its ___ joints and above a broad base of support.

hip

Describe the conditions for a system to be in stable equilibrium.

A system is in stable equilibrium if, when displaced from equilibrium, it experiences a net force or torque in a direction opposite to the direction of the displacement, resulting in a restoring force that moves it back toward the equilibrium position.

How can the stability of a human standing be increased?

The stability of a human standing can be increased by spreading the feet apart to widen the base of support and by lowering the center of gravity by bending the knees.

What is the first step in solving a static equilibrium problem?

a) Determine if the system is in static equilibrium

b) Draw a free body diagram

c) Apply the conditions for equilibrium

d) Check the solution for reasonableness

a) Determine if the system is in static equilibrium

In a static equilibrium problem, why is it useful to choose a pivot point where unknown forces cause zero torque?

a) It simplifies calculations

b) It increases the number of unknowns

c) It makes the problem more complex

d) It changes the direction of forces

a) It simplifies calculations

What happens to the forces exerted by the hands when a pole vaulter holds a pole with its center of gravity to the left of the person?

a) The right hand pushes down and the left hand pushes up

b) Both hands exert equal forces

c) The left hand pushes down and the right hand pushes up

d) The forces remain unchanged

a) The right hand pushes down and the left hand pushes up

In static equilibrium, the net force and net torque are both equal to ___.

zero

A free body diagram should include all forces, their magnitudes, directions, and points of ___.

application

Explain how the distribution of forces changes when a pole vaulter holds a pole with its center of gravity near one hand.

When the center of gravity is near one hand, that hand supports more of the pole's weight, resulting in unequal forces exerted by the hands. The hand closer to the center of gravity exerts a greater force.

What is the mechanical advantage (MA) of a simple machine?

a) The ratio of input force to output force

b) The ratio of output force to input force

c) The sum of input and output forces

d) The difference between input and output forces

b) The ratio of output force to input force

Which of the following is NOT a simple machine?

a) Lever

b) Pulley

c) Crank

d) Motor

d) Motor

In a lever, what is the point called where the lever pivots?

a) Fulcrum

b) Load

c) Effort

d) Arm

a) Fulcrum

What is the mechanical advantage of a wheelbarrow if the input lever arm is 1.02 m and the output lever arm is 0.075 m?

a) 0.073

b) 13.6

c) 1.36

d) 0.75

b) 13.6

What is the primary function of an inclined plane?

a) To change the direction of a force

b) To multiply force

c) To reduce the input force needed

d) To increase speed

c) To reduce the input force needed

A lever is a simple machine that consists of a rigid bar pivoted at a fixed point called the ___.

fulcrum

The mechanical advantage of a pulley system is approximately equal to the number of cables pulling directly ___ on the system.

upward

Describe the mechanical advantage of an inclined plane and how it affects the input force.

The mechanical advantage of an inclined plane allows a smaller input force to be used over a longer distance to move an object to a higher elevation. This reduces the input force needed compared to lifting the object directly upward.

What is the primary reason skeletal muscles exert larger forces within the body than the limbs apply to the outside world?

a) Muscles are attached close to joints via tendons.

b) Muscles are stronger than bones.

c) Muscles have a higher density than bones.

d) Muscles can expand beyond their resting length.

a) Muscles are attached close to joints via tendons.

How does bad posture cause back strain?

a) It increases the mechanical advantage of back muscles.

b) It creates a clockwise torque around the hips.

c) It decreases the force exerted by the lower back muscles.

d) It aligns the body's center of gravity with the base of support.

b) It creates a clockwise torque around the hips.

What is a benefit of having skeletal muscles attached close to joints?

a) Increased strength

b) Increased speed and agility

c) Reduced muscle fatigue

d) Improved balance

b) Increased speed and agility

Muscles can only ___, so they occur in pairs.

contract

The force the biceps muscle can exert depends upon its ___; it is smaller when it is shorter than when it is stretched.

length

Explain why lifting with your back can cause muscle strain and damage.

Lifting with your back creates abnormally large forces in the back muscles and spine, leading to strain and potential damage to discs and vertebrae.

Discuss the complexities in real systems of muscles, bones, and joints.

Real systems have complexities such as changing pivot points in joints, which alter lever arms and mechanical advantages, affecting the force exerted by muscles.