PHYS 1415 Ch 3

Kinetic energy equation

1/2mv^2

From the edge of a roof you throw a snowball downward that strikes the ground with 100 J of kinetic energy. Then you throw a second snowball upward with the same initial speed, and this too falls to the ground. Neglecting air resistance, the second snowball hits the ground with a kinetic energy of

100 J

A 2-kg mass that weighs 20 N has 40 J of potential energy relative to the ground. What is its height...what equation is used?

Conservation of Energy (Potential Energy)

The amount of potential energy possessed by an elevated object is equal to

Relative to a chosen reference level, equal to the kinetic energy it will acquire when freely falling to its reference level, and equal to the work done in lifting it

Energy cannot be created a destroyed. True or False

True

Efficiency equation (power)

Useful power output / total power input

Work equation

W=Fd

A car moving at 50 km/h skids with locked brakes. How far will it skid if it's initial speed is 150 km/h...what equation is used?

Work = Change in KE

Which has the greater momentum when moving? A bullet

either of these depending on speed

Impulse equation

force x time

A block of ice sliding down an incline has half its maximum kinetic energy

halfway down

The speed of a bullet fired from a gun will be about the same as the speed of the recoiling gun

if the masses of the bullet and gun are equal

A cannonball fired from a long-barrel cannon will have a greater muzzle velocity because the cannonball receives a greater

impulse

The change in momentum of an object is equal to the

impulse that acts on it

An iron ball and wooden ball of the same size are dropped simultaneously from a tower and reach the ground at the same time. The iron ball has a greater

momentum

momentum equation

momentum = mass x velocity

Consider a gun with a pellet that is more massive than the gun. The firing speed is greater for the

recoiling gun

Compared with falling on a stone floor, a wine glass may not break when it falls on a carpeted floor because the

stopping time is longer on the carpet

To catch a fast-moving ball, you extend your hand forward before contact with the ball and let it ride backward in the direction of the ball's motion. Doing this reduces the force of contact on your hand principally because the

time of catch is increased

A 1000-kg car and a 2000-kg car are hoisted to the same height. Raising the more massive car requires

twice as much work

When you ride your scooter you have momentum. When you ride twice as fast you have

twice the momentum

Change in momentum equation

Force x Time = final momentum - initial momentum

Whether a truck comes to a stop by crashing into a haystack or a brick wall, the impulse is

Greater with the haystack and brick wall

When a bus brakes to a stop it's kinetic energy transforms to

Heat

1000-kg truck moving at 10 m/s that brakes to a stop in 5 s has an average braking force of...what equation?

Impulse = Change in momentum

A boxer punches a sheet of paper in midair and brings it from rest up to a speed of 40 m/s in 0.05 s. If the mass of the paper is 0.01-kg, the force of the punch on the paper is...what equation is used?

Impulse = Change in momentum

Two identical freight cars roll without friction towards each other on a level track. One car rolls at 2 m/s and the other car rolls at 1 m/s. After the cars collide they couple and roll together with a speed of...what equation is used?

Inelastic Conservation of Linear Momentum (both objects in motion)

A sandbag is motionless in outer space. A second sandbag with 3 times the mass moving at 12 m/s collides with it and they both stick together and move at a speed of...what equation is used?

Inelastic Conservation of Linear Momentum Equation (one object at rest)

A 5000-kg freight car collides with a 10,000-kg freight car at rest. They couple upon collision and move at 2 m/s. What was the initial speed of the 5000-kg car...what equation is used?

Inelastic Conservation of Momentum

Inelastic conservation of linear momentum equation (both objects moving)

Initial Momentum 1 - Initial Momentum 2 = Final Momentum

Inelastic conservation of linear momentum equation (one object at rest)

Initial Momentum = Final Momentum

Elastic Conservation of Linear Momentum

Initial m1 x v1 + Initial m2 x v2 = final m1 x v1 + final m2 x v2

If you push for an hour against a stationary wall, you do no work

On the walk

Power equation

P=W/t

potential energy Equation

PE=mgh

The order in which solar energy is converted to the kinetic energy of an automobile is

Photocells, electrolysis, fuel cells, motor, kinetic energy

In raising a 5000-N piano with a pulley system, for every 1 m of rope pulled down, the piano rises 0.1 m. Ideally, this means the force needed to lift the piano is...what equation is being used?

Power Equation

The source of Earth's internal energy involves

Radioactivity

conservation of energy equation

KEi + PEi = KEf + PEf

A shopping cart moves with a kinetic energy of 40-J. If it moves at twice the speed, it's kinetic energy is...what equation is used?

Kinetic Energy

A 30-kg girl and a 25-kg boy face each other on friction-free roller blades. The girl pushes the boy, who moves away at a speed of 1.0 m/s. The girl's speed is...what equation is used?

Elastic Conservation of Linear Momentum

An astronaut floating in outer space throws a baseball. If the ball moves away at 20 m/s, the astronaut will move in the opposite direction at...what equation?

Elastic Conservation of Linear Momentum