Chapter 6
A fluid can be either a liquid or a gas
True
A rocket ship is pushed forward by gases that are forced out the back of the ship
True
The combination of all the forces that act on an object is called the net force.
True
The net force on an objecting falling at terminal velocity is zero
True
You are on a frozen pond, and the ice starts to crack. If you lie down on the ice and begin to crawl, this will
decrease the pressure on the ice.
Accelerations are produced by
forces
A cart is pushed and undergoes a certain acceleration. Consider how the acceleration would compare if it were pushed with twice the net force while its mass increased by four. Then its acceleration would be
half
The reason a 20-kg falls no faster than a 10-kg rock in free fall is that
the force/mass ratio is the same
When you stand on one foot instead of two, the pressure you exert on the ground is
twice
A push on a 1-kilogram brick accelerates the brick. Neglecting friction, to equally accelerate a 10-kilogram brick, one would have to push
with 10 times much force
A sportscar has a mass of 1500 kg and accelerates at 5 meters per second squared. What is the magnitude of the force acting on the sportscar?
7500 N (show work)
If the force acting on a cart doubles, what happens to the cart's acceleration?
It doubles
If the force acting on a cart quadruples what happens to the cart's acceleration?
It quadruples
Friction is a force like any other force and affects motion. Friction occurs in
Solids sliding over one another. Fluids Air
A girl pulls on a 10-kg wagon with a constant force of 20 N. what is the wagon's acceleration?
2 m/s2 ( show work)
A jet has a mass of 40,000 kg. The thrust for each of four engines is 20,000 N. What is the jet's acceleration when taking off?
2 m/s2 (show work)
A tow truck exerts a force of 2000 N on a car, accelerating it at 1 m/s/s. What is the mass of the car?
2000 kg (show work)
Suppose the force of friction on a sliding object is 25 N. The force needed to maintain a constant velocity is
25 N
When a woman stands with two feet on a scale, the scale reads 280 N. When she lifts one foot, the scale reads
280 N
You pull horizontally on a 50 kg crate with a force of 450 N and the friction force on the crate is 250 N. The acceleration of the crate is
4 m/s2 ( Show work)
A jumbo jet cruises at a constant velocity when the total thrust of the engines on the jet is 50,000 N. How much air resistance acts on the jet?
50,000 N
A book weighs 4 N. When held at rest in your hands, the net force on the book is
0 N
An apple weighs 1 N. The net force on the apple when it is in free fall is
1 N
A 20-N falling object encounters 4 of air resistance. The magnitude of the net force on the object is
16 N (show work)
The acceleration produced by a net force on an object is...
1. Inversely proportional to the mass of the object 2. Directly proportional to the magnitude of the net force. 3. In the same direction as the net force
If a truck has ten times the mass of a car and the two vehicles are pushed with an equal force, you would expect the acceleration of the truck to be
1/10 times that of the car.
A 10-kg brick and 1-kg book are dropped in a vacuum. The force of gravity on the 10-kg brick is
10 times as much as the force on the 1-kg book F x g= w
A box is dragged without acceleration in a straight-line path across a level surface by a force of 13 N. What is the frictional force between the box and the surface?
13 N
Excluding the force due to air pressure there is only one force acting on a book lying at rest on a tabletop.
False
Is it possible for an object in free fall to have zero acceleration
False
The acceleration of an object is inversely proportional to the net force acting on it.
False
The speed of an object dropped in air will continue to increase without limit
False
A heavy person and a light person and a light person parachute together and wear the same size parachutes. Assuming they open their parachutes at the same tim, which person reaches the ground first?
The heavy person bc of greater terminal velocity