### the impulse of an object can change if:

the object's mass changes and if the object's velocity changes

### A rifle recoils while firing a bullet. The speed of the rifle's recoil is small because the ____.

rifle has much more mass than the bullet

### Two objects have the same size and shape, but one is much heavier than the other. When they are dropped simultaneously from a tower, they reach the ground at the same time, but the heavier one has a greater ____.

momentum

### In order to catch a ball, a baseball player extends the hand forward before impact with the ball and then lets it ride backward in the direction of the ball's motion. Doing this reduces the force of impact on the player's hand principally because the ____.

time of impact is increased

### When you are in the way of a fast moving object and can't get out of its way, you will suffer a smaller force of impact if you decrease its momentum over a ___.

long time

### A car traveling along the highway needs a certain amount of force exerted on it to stop in a certain distance. More stopping force is required when the car has ___.

more mass, more momentum, and less stopping time

### A bullet is fired from a gun. The speed of the bullet will be about the same as the speed of the recoiling gun if ____.

the mass of the bullet equals the mass of the gun

### Padded dashboards in cars are safer in an accident than non-padded ones because an occupant hitting the dash has ____.

increased time of impact

### The force of an apple hitting the ground depends upon ____.

the speed of the apple just before it hits; the time of impact with the ground; and whether or not the apple bounces

### Compared to falling on a stone floor, a glass may not break when it falls on a carpeted floor because the ____.

carpet provides a smaller impulse and a longer time

### A heavy truck and a small car rolling down at the same speed are forced to stop in the same amount of time. Compared to the force that needs to stop the car, the forced needed to stop the truck is ___.

greater

### A karate expert executes a swift blow and breaks a cement block with her bare hand. The magnitude of the force experienced by her hand is ____.

identical to the force applied to the block

### You're driving down the highway and a bug spatters into your windshield. This is an example of a ___.

inelastic collision

### If you push for half an hour or a whole hour against a stationary wall how much work is done?

no work is done in either case

### If you push an object twice as far while applying the same force, how much work do you do?

twice as much work

### If you push an object a given distance, while applying twice the force how much work is done?

twice as much work

### If you do work on an object in 1/3 the usual time, your power output is ___.

3 times the usual power output

### An object lifted 10 meters gains 200 J of potential energy. If the same object is lifted 20 meters its potential energy gain is ____.

twice as much

### A 1000-kg car and a 2000-kg car are hoisted the same distance. Raising the more massive car requires ___.

twice as much work

### A bow is drawn so that it has 40 J of potential energy. When fired, the arrow will ideally have a kinetic energy that is ___.

40 J

### After rolling halfway down an incline, a marble's kinetic energy is ____.

the same as its potential energy

### Neglecting friction, a small ball; and a similar large ball, at rest, are allowed to roll down and incline for only one second. At this instance, the large ball will have a greater ____.

potential energy; kinetic energy; and speed

### What tasks requires the most work: lifting a 50-kg sack 2 meters or lifting a 25-kg sack 4 meters?

they are the same

### Both a 50-kg sack is lifted 2 meters from the ground and a 25-kg sack is lifted 4 meters in the same time. The power exerted in raising the 50-kg sack is ___.

the same

### A 2-kg mass is held 4 m above the ground. What is the approximate potential energy of the mass with respect to the ground?

80 J

### Using 1000 J of work, a toy elevator is raised from the ground floor to the second floor in 20 seconds. The power needed to do this job is ____.

50 W

### How much power is used if a force of 35 N is used to push a box a distance of 10 m in 5 seconds?

70 W

### rotational speed

sometimes called angular speed; involves the # of rotations or revolutions per unit of time

### rotational inertia

the property of an object that measures its resistance to any change in its state of rotation: if at rest, the body tends to remain at rest; if rotating it tends to remain rotating and will continue to do so unless acted upon by an external net torque

### center of mass (CM)

the average position of the mass of an object; moves as if all the external forces acted at this point

### center of gravity (CG)

the average position of weight or the single point associated with an object where the force of gravity can be considered to act

### centripetal force

a force directed toward a fixed point, usually the cause of circular motion means "center seeking" or "toward the center"

### centrifugal force

an outward force apparent in rotation frame of reference. It is apparent in the sense that it is not part of an interaction but as a result of rotation-- which no reaction-force counterpart

### angular momentum

the product of the body's rotational inertia and rotational velocity about a particular axis. For an object that is small compared with the radial distance, it can be expressed as the product of mass, speed, and the radial distance of rotation

### conservation of angular momentum

When no external torque acts on an object or a system of objects, no change of angular momentum can occur hence, the angular momentum before an event involving only internal torques or no torques to the angular momentum after the event

### name the action and reaction: a hammer hits a nail

action: hammer hitting nail

reaction: nail resisting hammer

### name the action and reaction: earth's gravity pulls down on a book

action: earth's gravity pulls down on book

reaction: book pulling earth towards it

### name the action and reaction: a helicopter blade pushes air downward

action: helicopter blade pushes air downward

reaction: air pulls blade toward it

### name the action and reaction: you step off of a curb

action: earth pulling your down

reaction: the ground pulling towards you

### name the action and reaction: you pat your little sister on the back

action: you pat your little sister on the back

reaction: your sister's back pushes back on your hand

### name the action and reaction: a wave hits the shore

action: a wave hits the shore

reaction: the shore pushes the wave back

### name the action and reaction: a baseball bat hits a baseball

action: a baseball bat hits a baseball

reaction: baseball pushes back on the baseball bat

### When you push against the wall with your fingers, they bend because the experience a force. Identity this force.

Reaction (action-reaction)