PHY 205 Lecture Notes - Lecture 52: Friction, Net Force, Moment Of Inertia

Match the following words with their descriptions:

1. Speed 2, Velocity 3, Acceleration 4. Force 5. Mass 6. Inertia

Rate at which an object covers a distance, disregarding direction.

Rate at which an object covers a distance in a given direction.

The tendency of objects to not change their state of motion unless acted on by an outside force.

Measure of the amount of matter in an object.

Rate at which an object changes its velocity.

A push or pull on an object, that when unopposed, results in a change in the object's state of motion.

1. Which of the following describes an object with a non-zero netforce acting on it? Choose all that apply.
The moped accelerated while making a left turn.
The motorcycle traveled at a constant speed while making au-turn.
The truck slowed down while making a right turn.
The spaceship traveled at a constant speed in a straightline.
The car sped up from 50 mph to 65 mph while moving in a straightline.

2. If you observe that an object is accelerating, what should youconclude?
A non-zero net force is acting on it. Only forces causeacceleration. As such, if an object is accelerating it must bebecause a non-zero net force is acting on it.
It must be in free fall.
It must be changing direction. Acceleration is a vector and vectorshave both magnitude and direction. Thus if an object isaccelerating it must be changing direction.
The forces acting on the object must be greater than the forces theobject is exerting.
It must be speeding up. If an object is accelerating that means itis speeding up.

3. Which of the following are true according to Newton's 2nd Law?Choose all that apply.

If the acceleration is zero, then the net force is zero.
If you apply the same force to 2 objects, the one with more masswill have a greater acceleration.
If you apply the same force to 2 objects, the one with less masswill have a greater acceleration.
If two objects have the same acceleration, the one with less masswill have a larger net force exerted on it.
If two objects have the same acceleration, the one with more masswill have a larger net force exerted on it.
The larger the net force on an object is, the larger theacceleration.
The larger the net force on an object is, the smaller theacceleration.

4. A box is on the Moon. The box weighs 152 lb and is in free fall.How much force is the box exerting on the Moon and in whatdirection?

lb
Up
Down
Right
North
East
West
Left
South

5. Which of the following are the correct units for mass? Chooseall that apply.
slugs
u
kg·m/s2
g
N
m/s2
oz
lb

6. If an object is traveling in a circle, which of the followingmust be TRUE? Choose all that apply.
The object is slowing down.
The object is speeding up.
The object has a net force acting on it.
The object has a constant velocity.
The object is accelerating.

1. The SI unit of force, newton, is a compound unit, which can be written as _____.

2. According to the Newton's 2nd Law of Motion, when forces exerted on an object are not balanced, the object will accelerate.

• True
• False

3. An object with mass 27.7 kg is suspended at rest on a string, what is the tension force magnitude (in unit of newton) in the string?

4. In the equation , represents the sum of all forces on an object.

• True
• False

5. An object moving with a constant velocity will experience ______ net force.

• nonzero
• zero
• imaginary

6. Assuming that a constant net force is applied to an object, if the mass of the object increases then the acceleration will ____.

• increase
• decrease
• stay the same