Physics Unit E (only the ones i struggle with)

a .140 kg baseball is dropped and reaches a speed of 1.20 m/s just before it hits the ground. It rebounds with the speed of 1.00 m/s. What is the change of the ball's momentum

.308 kgm/s upwards

A 900 kg car traveling east at 15.0 m/s collide with a 750 kg car traveling N at 20.0 m/s. The cars stick together. In what direction does the wreckage move just after the collision?

48 degrees N of E

A 2.00 g bullet hits and becomes embedded in a 5.00 kg wood block which is hanging from a 1.20 m long string. This causes the block to swing through an arc 3.5 degrees. What was the speed of the bullet before it hit the block?

524 m/s

Describe elastic and inelastic collision

Elastic----KE is conserved and P is conserved Inelastic------- P is conserved Perfectly Inelastic----final velocities are same

equation for impulse

I= Ft= change in p= pf-pi---measured in kgm/s

K

K=k1+k2...

what is the equation for relating k to p

K=p^2/2m

P equation

P= p1+p2...

What is the equation for conservation of momentum in 2D

Pi=Pf Pix=Pfx Piy=Pfy

conservation of momentum equation

Pi=Pf because change of P is 0 (constant speed or not moving) or Fnet is 0

An artillery shell explodes in midair and breaks up into many fragments. Which of the following statements are true regarding conditions immediately before and immediately after the explosion: I. The total momentum of the fragments is equal to the original momentum of the shell. II. The total kinetic energy of the fragments is equal to the original kinetic energy of the shell.

Statement 1 only

Impulse-momentum relationship

The greater the impulse exerted on something, the greater will be the change in momentum of that something

What is the equation for the velocity of a the Cm of a multiple mass system?

Vcm= m1v1+m2v2/m1+m2

How do you calculate the CM

Xcm= m1x1+m2x2/m1+m2 (this is the same for y)

What is the equation for the acceleration of a the Cm of a multiple mass system?

aCM = m1a1+m2a2/m1+m2

The equation for acceleration

aCM=Fnet/M (Center of mas follows Newton's 2nd Law)

in a collision between 2 unequal masses how does the impulse imparted to the smaller mass by the larger mass compare with the impulse imparted to the larger mass by the smaller one

equal

Identical forces act for the same length of time on two different objects. The magnitude of the change in momentum of the lighter object is

equal to the change in momentum of the larger mass but not zero

a rope is held from one end in such a way that the lower end just touches a table. The rope is then lowered onto the table with constant velocity. The force that is needed to hold the upper end of the rope is ______

equal to the weight of the portion of the rope that is not on the table

A system that had zero momentum must also have zero kinetic energy

false

Internal forces cannot change the total kinetic energy system

false

The impulse delivered to an object is equal to the change in the object's velocity

false

How do you find Impulse without a constant force

find the area of a Ft graph (and Area/time=F)

To find the center of mass of irregular shapes you ....

find the x/y coordinates of the shape to find the center of mass

The ____ mass has greater p or I if the kinetic energy is the same

greater

A rope is lying on a table. You pick up one end and start raising it with a constant velocity. The force you have to exert on the rope is ____

greater than the weight of the part of the rope that is not touching the table

Impulse/moemtum

how force applied over a period of time changes an object's velocity, and the various form of interaction between two objects.

Stability

if the vertical line of the center of mass is beyond the supporting point, the object will become unstable and tips over.

If 2 stars have the same mass where is the center of mass?

in the middle

Internal force does effect the _______ objects momentum

individual

a railroad car of mass m and speed v collides and sicks to an identical railroad car that is initially0 at rest. After the collision the KE of the system

is 1/2 as much as before (double the mass in an inelastic collision is 1/2 velocity)

A freight car moves along a frictionless level railroad track at constant speed. The car is open on top. A large load of coal is suddenly dumped into the car. What happens to the velocity of the car?

it decreases (if the weight is m/2 then the final velocity is 2/3)

k equation

k=1/2mv^2= J= kgm^2/s^2= N/m= mg/m-----scalar

KE is never ____

negative (becuase v^2 is always pos)

p equation

p=mv=kgm/s---vector

What is the equation for relating p to k

p=square root2mK

The ____ mass has greater Kinetic Energy if the momentum is the same

smaller

two different masses have equal non zero kinetic energies. The momentum of the smaller mass is

smaller than the momentum of the larger mass

The Cm of an irregular shape object follows a _______

smooth trajectory

A rubber ball and a lump of putty have equal mass. They are thrown with equal speed against a wall. The ball bounces back with nearly the same speed with which it hit. The putty sticks to the wall. Which objects experiences the greater momentum change?

the ball

Jacques and George meet in the middle of a lake while paddling in their canoes. They come to a complete stop and talk for a while. When they are ready to leave, Jacques pushes George's canoe with a force to separate the two canoes. What is correct to say about the final momentum and kinetic energy of the system?

the final momentum is zero kgm/s but the KE is positive

A tennis ball undergoes an elastic collision when it hits the ground and bounces up. It is given that the speed of the ball just before it hits the grounds is -v0 and immediately after the rebound it is +v0. What causes this

the momentum of the ball changes and the momentum of the Earth also changes by the same amount

Center of mass

the point in an object that moves as if all the object's mass were concentrated at that point. At the Cm the object can be balance

define momentum

the quantity of motion of a moving body, measured as a product of its mass and velocity.

When 2 objects collide the momentum change is ____

the same in magnitude but opp. in direction (cons. of momentum)

The internal force does not effect the ______ system of momentum and only ______ effects P

total; F (external)

If star 1 has more mass than star 2 where is the center of mass?

towards the heavier mass or in the center of the heavier mass

A particle that has zero momentum must also have zero kinetic energy (T or F)

true

Internal forces cannot change the total momentum of a system

true

the net force acting on an object is equal to the rate of change of its momentum

true

* If m1 = m2 , v1i = v0, v2i = 0 * If m1 >> m2 , v1i = v0, v2i = 0 * If m1 << m2 , v1i = v0, v2i = 0

v1 = 0, v2 = v0 v1 = v0, v2 = 2v0 v1 = - v0, v2 = 0

What is the general solution for elastic collision when v1=v0 and v2i=0

v1= (m1-m2/m1+m2)v0 v2= (2m1/m1+m2)v0

What is the general solution for elastic collision when v1 and v2 initially is not 0

v1=(m1-m2/m1+m2)v1i + (2m2/m1+m2)v2i v1=(m2-m1/m1+m2)v2i + (2m1/m1+m2)v1i