Chapter 2,3,6,7

What equation would you use: A 60 kg person on in line skates pushes against a wall with a force of 30 N and recoils. What acceleration does that person experience?

A = f/m (30/60)

A pair of parallel forces of 8 N and 12 N can have a resultant of

Either 4 N or 12 N

T or F: A scalar quantity has both magnitude and direction, whereas a vector quantity is described by only its direction.

False

T or F: Air resistance is cause by friction between the air and an object moving through the air

False

T or F: An airplane in an acrobatic loop-the-loop maneuver is in dynamic equilibrium if the speed is constant

False

T or F: If a hockey puck slides on a perfectly frictionless surface, it will eventually slow down because of its inertia

False

T or F: Objects move only when a force is exerted

False

T or F: The SI unit force is called the kilogram

False

T or F: The acceleration of an object is inversely proportional to the net force acting on it

False

T or F: The amount of matter in an object is called its weight

False

T or F: if a bicycle and a parked car have a head on collisioin, the force of impact is greater on the bicycle

False

Whirl a rock at the end of a string and it follows a circular path. If the string breaks, the tendency of the rock is to

Follow a straight line path

What equation would you use: A 230 kg bear grasping a vertical tree slides down at constant velocity. What is the friction between the tree and the bear?

Force= mg

When Nellie hangs suspended from a pair of ropes that are not vertical, the tension in each rope will be

Half her weight

When you stand on two bathroom scales, one foot on each scale with weight evenly distributed, each scale will read...

Half your weight

what equation would you use: On the surface of Jupiter the acceleration due to gravity is about 3 times that on earth. How much would a 100 kg rock weigh on Jupiter?

W = mg (100)(3x10) 3,000 N

What equation would you use: You push with 30 N on a 3 kg block and there are no opposing forces. What is the block's acceleration?

A = F/M (30/3 = 10)

Burl and Paul have a total weight of 1300 N. The tensions in the supporting ropes that support their scaffold add to 1700 N. The weight of the scaffold itself must be

400 N . (1700 N - 1300 N = 400 N)

static equilibrium

objects at rest

What equation would you use: The following forces act on an object: 20 N north, 50 N south, and 40 N west. What is the magnitude of the net force

- 50-20 (because opposite direction) - Pythag theory

A high school student hits a nail with a hammer. During the collision, there is a force

on the nail and the hammer

The equilibrium rule (sig)F = 0, applies to

- objects or systems at rest - objects or systems in uniform motion in a straight line - Scalar quantities

If you push off the ground with a force of 350 N when you jump upward, what force pushes Earth downward?

350 N

A woman weighing 500 N sits on the floor. she exerts a force on the floor of

500 N

As a 500 N woman sits on the floor, the floor exerts a force on her of

500 N

The law of inertia states that an object

-at rest will remain at rest unless acted on by an outside force - Will continue moving at the same velocity unless an outside force acts on it - Will continue moving in a straight line unless an outside force acts on it

The acceleration produced by a net force on an object is

-directly proportional to the magnitude of the net force - In the same direction as the net force - inversely proportional to the mass of an object

A girl whose weight is 200 N hangs from a bar supported by two strands of rope. What is the tension in each strand?

100 N

What equation would you use: On the surface of Jupiter, the acceleration due to gravity is about 3 times that of the earth. What would be the mass of a 170 kg rock on Jupiter?

170 kg MASS DOESN'T CHANGE

A 10-N force and a 30-N force act on an object in opposite directions. What is the net force on the object?

20 N

What equation would you use: You push with 27 N on a 10 kg chest and there is a 7 N force of friction. How fast will the chest accelerate?

27-7 = 20 --> a =f/m

What equation would you use: A boxer punches a sheet of paper in midair, and brings it from rest up to a speed of 40 m/s in .05 s. If the mass of the paper is .01 kg, what is the force of impact on the paper?

A= V(f) - V(i)/ t F = ma

What equation would you use: You push with 10 N on a 5 kg block and there are no opposing forces. How fast will the block accelerate?

A=f/m

Consider a pair of parallel vectors, one of 5 N and the other of 12 N, both acting on the same object. Show that the net force on the object can be either 7 N or 17 N.

Add: 5 + 12 = 17 Subtract: 12 - 5 = 7

Whenever an object exerts a force on another object, the second object exerts a force of the same magnitude, but in the opposite direction to that of the first object

Always true

The law of inertia applies to

Moving objects and objects at rest

Which has more mass, a kilogram of feathers or a kilogram of iron?

Neither. The masses are equal

A tennis ball and a solid steel ball the same size are dropped at the same time. In the absence of air resistance, which ball has the greater acceleration?

Nonsense! They both have the same acceleration

dynamic equilibrium

Objects moving at constant speed in a straight-line path

The astronomer Copernicus was the first person to publicly state that the earth

revolves around the sun

When you press a coiled spring downward, the spring presses upward on your hand with...

The same amount of force

A tennis ball and a solid steel ball the same size are dropped at the same time. Which ball has the greater force acting on it?

The steel ball

Galileo found that a ball rolling down one inclined plane would roll how far up another inclined plane?

To nearly the same height as where it originally started

T or F: A rocketship is pushed forward by gases that are forced out the back of a ship.

True

T or F: An object can be in equilibrium whether it is at rest or moving steadily at constant speed in a straight line

True

T or F: Inertia is the reluctance any material object has to change in its state of motion

True

T or F: The earth and moon pull on each other with equal amounts of force

True

T or F: Whenever one object exerts a force on a second object, the second object always exerts the same amount of force back on the first object

True

T or F: the combination of all the forces that act on an object is called the net force

True

T or F: the net force on an object is the combination of all forces that act on it

True

What equation would you use: A fighter punches a sheet of paper in midair, and brings it from rest up to a speed of 40 m/s in 0.08 s. What is the force of impact on the paper if the mass of the paper is 0.01 kg?

V(f) - V(i)/t --> f= ma

How do you solve: A 50 kg block of cement is pulled upward with a force of 600 N. What is its acceleration?

W = MxG --> 600 N - 500 N = 100 N --> A= F/M (100/50)

After a cannonball is fired into frictionless space, the amount of force needed to keep it equals

Zero, since no force is necessary to keep it moving

As he falls from a high-flying stationary helicopter, Bronco's velocity increases and his acceleration

decreases

Suzie holds an apple at rest in her outstretched hand. The force she applies in holding it still

equals the weight of the apple

Newton's first law of motion

every object continues in a state of rest, or of uniform speed in a straight line, unless acted on by a nonzero net force.

Forces always occur

in pairs

If the force acting on a cart doubles, what happens to the cart's acceleration?

it doubles

An unfortunate bug splatters against the windshield of a moving car. Compared to the deceleration of the car, the deceleration of the bug is

larger

An unfortunate bug splatters against the windshield of a moving car. Compared to the force of the car on the bug, the amount of force of the bug on the car is

larger

Newton's second law of motion

the acceleration produced by a net force on an object is directly proportional to the magnitude of the net force, is in the same direction as the net force, and is inversely proportional to the mass of the object (A=F/M)

The number of forces that act on a bag of sugar suspended by a weighing scale are

two

What equation would you use: On the surface of Jupiter, the acceleration due to gravity is about 3 times that on earth. how much would a .40 kg rock weigh on Jupiter?

w = mg --> w=.40x30

What equation would you use: A person weighs 650 N. What is the mass of the person?

w= mg --> m=w/g (650/9.8)

What equation would you use: How much does a 10 kg bag of grass seed weigh?

weight =mg

Newton's third law of motion

whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first object.