Forces Test--Physics
Draw a free body diagram of an athlete running along a horizontal track.
(instead of friction it would be air resistance)
Four forces act on a hot air balloon, shown from the slide in the figure below. Find the magnitude and direction of the X and Y forces on the balloon.
(up 5120 N, down 4050 N, left 1520 N, right 950 N) Fy= 1070 N up Fx= 570 N left
A 0.150 kg baseball is thrown upward with an initial speed of 20.0 m/s. What is the net force on the ball when it reaches its peak?
0 N
A 95 kg clock initially at rest on a horizontal floor requires a 650 N horizontal force to set in motion. After the clock is in motion, a horizontal force of 560 N keeps it moving with a constant velocity. Find the coefficient of static friction and the coefficient of kinetic friction.
0.69, 0.60
A 5.0 kg bucket of water is raised from a well by a rope. If the upward acceleration of the bucket is 3.0 m/s^2, find the force exerted by the rope on the bucket of water.
15 N
What acceleration will you give to a 24.3 kg box if you push it horizontally with a net force of 85.5 N?
3.5 m/s^2
What net force is required to give a 25 kg suitcase an acceleration of 2.2 m/s^2 to the right?
55 N
A block with a mass of 6.0 kg is held in equilibrium on an incline at an angle of 30 degrees. Find the magnitude of the normal force on the block.
58.8 N
Two lifeguards pull on ropes attached to a raft. If they pull in the same direction, the raft experiences a net force of 334 N to the right. If they pull in opposite directions, the raft experiences a net force of 106 N to the left. A. Draw a free body diagram representing the raft for each situation. B. Find the force exerted by each lifeguard on the raft for each situation.
A. (two arrows in same direction going to the right) (Two arrows in opposite directions [left + right]) B.
An 1850 kg car is moving to the right at a constant speed of 1.44 m/s. What is the net force on the car? (A) What would be the net force on the car if it were moving to the left? (B)
A. 0 N B. 0 N
A 1250 kg car is pulling a 325 kg trailer. Together, the car and the trailer have an acceleration of 2.15 m/s^2 directly forward. A. Determine the net force on the car. B. Determine the net force on the trailer.
A. 2687.5 N B. 698.75 N
A 2.26 kg book is dropped from a height of 1.5 m. A. What is its acceleration? B. What is its weight in newtons?
A. 9.81 m/s^2 B. 22.17 N
A large crate is placed on the bed of a truck, but it is not tied down. A. As the truck accelerates forward, the crate slides across the bed until it hits the tailgate. Explain what causes this. B. If the driver slammed on the brakes, what would happen to the crate?
A. Inertia--resistance of an object to move B. The crate would move forward until hitting an object that has a greater mass to stop it.
a form of friction whenever an object moves through a fluid medium such as air or water the fluid provides a resistance to the object's motion
Air Resistance
A sky diver falls through the air. As the speed of the sky diver increases, what happens to the sky diver's acceleration? What is the acceleration when the sky diver reaches terminal speed?
As speed increases, air resistance increases therefore acceleration would decrease.
Pushes/pulls requiring physical contact between the objects. - ex. baseball and bat
Contact forces
The force that attracts Earth to an object is equal to and opposite to the force that Earth exerts on the object. Explain why Earth's acceleration is not equal and opposite the object's acceleration.
Earth's mass is so much larger than the object's mass
Objects create force fields that act on other objects - ex. gravity, static electricity, magnetism
Field Forces
A dog pulls on a pillow with a force of 5 N at an angle of 37 degrees above the horizontal. Find the X and Y components.
Fx= 3.01 N Fy= 3.99 N
the force that opposes the movement of two surfaces that are in contact and are sliding over each other
Kinetic Friction
_________ friction is always less than the maximum _______ friction
Kinetic, static
What physical quantity is a measure of how much inertia an object has?
Mass...The more mass an object has, the harder it is to move that object.
Which is usually greater, the maximum force of static friction or the force of kinetic friction?
Maximum static friction
An object at rest remains at rest and an object in motion continues in motion with constant velocity (that is, constant speed in a straight line) unless the object experiences a net external force.
Newton's First Law of Motion
The acceleration of an object is directly proportional to the net force acting on the object and inversely proportional to the object's mass.
Newton's Second Law of Motion
If two objects interact, the magnitude of the force exerted in object one by object two is equal to the magnitude of the force simultaneously exerted on object two by object one and these two forces are opposite in direction. In other words, for every action, there is an equal and opposite reaction.
Newton's Third Law of Motion
If an object is at rest can we conclude that no external forces are acting on it?
No. When an object is at rest, all of the forces that are acting upon the object are at equilibrium.
Acts on a surface in a direction perpendicular to the surface
Normal Force
A beach ball is left in the bed of a pickup truck. Describe what happens to the ball when the truck accelerates forward.
The ball would move backwards
State Newton's second law of motion in your own words.
The force is equal/proportionate to the mass and acceleration of an object.
coefficient of kinetic friction
Uk= Fk/ Fn
The gravitational force (Fg) exerted on an object by earth is a vector quantity, directed toward the center of Earth.
Weight
Is it possible for an object to be in motion if not net force is acting on it? Explain.
Yes because when an object is falling and the air resistance and gravity is equal, the net force is zero.
The quantity that expresses the dependence of frictional forces on the particular surfaces in contact
coefficient of friction
Velocity is ___________ because the net force is at zero.
constant
Fundamental forces (field forces)
electromagnetic, gravitational, strong nuclear, weak nuclear
To determine the direction of the force of static frication, use ________
equilibrium
the state in which the net force is zero
equilibrium
the tendency of an object to resist a change in motion
inertia
The force of ________ friction is always opposite the direction of motion
kinetic
sum of all forces
net force
The __________ __________ is equal and opposite to the component of gravitational force that is perpendicular to the contact surface
normal force
In free body diagrams, the force of friction is always __________ to the surface of contact
parallel
the force that resists the initiation of sliding motion between two surfaces that are in contact and at rest
static friction
coefficient of static friction
us= F s,max/ Fn