chapter 4 Flashcards
(38 cards)
An object of mass m sits on a flat table. The Earth pulls on this object with force mg, which we will call the action force. What is the reaction force?
The object pulling upward on the Earth with force mg.
As a car drives with its tires rolling freely without slipping, the type of friction acting between the tires and the road is usually ________
static friction
A hockey puck slides across the ice with a constant velocity. What is the net force acting on the puck?
zero
1st law of motion (law of intertia)
an object moves at a constant velocity (or stays at rest) as long as no net force acts on it
inertia
tendency of a body to maintain motion at constant velocity or at a state of rest (zero velocity)
an object at rest…
no net force is acting on it
an object moves with constant velocity..
no net force is acting on it
You put your book on the car seat next to you. When you hit the brakes suddenly, the book slides forward off the seat. When does this happen?
no net force acts on it
- book continued to move forward, which was its intail state of motion
You kick a smooth flat stone out on a frozen pond. The stone slides, slows down and eventually stops. What can you conclude?
A net force acted on it all along
2nd Law of Motion
The acceleration of an object is directly proportional to the net force (vector sum of the forces) acting on it and is inversely proportional to the objects mass
How much tension must a rope withstand if it is used to accelerate a 1210 kg car horizontally along a frictionless surface at 1.20 m/s^2?
F=ma
(1210 kg)(1.20 m/s^2) = 1452 N
A force F acts on mass m1 giving acceleration a1. The exact same force acts on a different mass m2 giving acceleration a2=2a1. If m1 and m2 are glued together and the same force F acts on this combination, what is the resulting acceleration?
-going to be smaller than a1
F=(m1+m2)a
F=(.5m1)(2a1)
2/3 a1
3rd Law of Motion
Whenever one object exerts a force on a second object, the second exerts an equal force in the opposite direction on the first.
Forces are associated with interactions between objects.
T/F
True
- action/reaction pair
A large truck collides head-on with a small compact car. During the collision,
Which of Newton’s laws best explains why motorists should buckle-up?
the first law
When you sit on a chair, the resultant (net) force acting on you is ________
zero
In the absence of an external force, a moving object will ________
move with a constant velocity.
A rocket moves through empty space in a straight line with constant speed. It is far from the gravitational effect of any star or planet. Under these conditions, the force that must be applied to the rocket in order to sustain its motion is _________
zero
You are standing in a moving bus, facing forward, and you suddenly fall forward. You could imply from this that the bus’s __________
velocity decreased.
A constant net force acts on an object. Describe the motion of the object.
constant acceleration
The acceleration of an object is inversely proportional to ________
its mass
A net force F acts on a mass m and produces an acceleration a. What acceleration results if a net force 2F acts on a mass 4m?
a/2
An object of mass m sits on a flat table. The Earth pulls on this object with force mg, which we will call the action force. In this case, what is the reaction force?
The object pulling upward on the Earth with force mg.
