Chp 7 Reading Assignment : Momentum Conservation

Rank the following football player collisions in order from the largest final momentum to the right (top), to the smallest final momentum to the left (bottom). Assume that the two players are stuck together after they collide.

1. 100kg full with 50kg 2. 100kg full with 75kg 3. 80kg full with 50kg at 8m/s 4. 80kg full with 50kg at 6m/s

Match the following collisions with the type of collision on the right.

1. A collision where no kinetic energy is lost and the objects bounce off each other.= elastic collision 2. A collision where the objects bounce off each other but lose some kinetic energy.= partially inelastic collision 3. A collision where the objects stick together after the collision.= perfectly inelastic collision

Match the causes in the left column with their effects in the right column.

1. Force=Change in velocity, called acceleration 2. Impulse= Change in the momentum 3. Work=Change in the kinetic energy

Match the following situations with the type of collision on the right.

1. Two pool balls collide and the total kinetic energy is conserved.= elastic collision 2. A car hits a truck and they bounce off of each other with major damage done to the car.= inelastic collision 3. A snowball hits another snowball in mid-air and they stick together.= perfectly inelastic collision

Two 180 kg astronauts in space float motionlessly. Astronaut 1 pushes the other (astronaut 2). The final momentum of astronaut 1 is 360 kg m/s to the right. The final momentum of astronaut 2 is kg m/s to the left.

360

A rifle fires a bullet. Which of the objects has the largest magnitude of momentum upon being shot? Assume the external forces are negligible.

Both have the same magnitude of momentum.

Two people (one large, one small) stand motionless on a frozen lake that is frictionless. They push off each other. Which of the following statements are correct?

Both people will feel the same magnitude of force. Both people will have the same magnitude of momentum. The total momentum of the two people after they push off each other will be zero.

A child stands next to a more massive adult on a frictionless frozen pond. The child pushes the adult. Which of the following statements are correct after the push?

The child travels with the greatest speed. Both the child and the adult travel with the same magnitude of momentum. The total momentum is zero.

A hard billiard ball elastically collides with another hard billiard ball of equal mass. Which situation is possible?

The first ball stops and the second ball moves with the same velocity as the first.

A rocket at rest in outer space fires a burst from its rockets. Which statements are true?

The momentum of the rocket exhaust is equal to the momentum of the rocket. The force the rocket exerts on the exhaust is equal to the force the exhaust exerts on the rocket. The total momentum after the burst is zero.

In which of the following situations is the collision inelastic of some type (perfectly or otherwise)?

The pool cue hits the seven ball on a pool table, but some kinetic energy is lost. A snowball hits and get stuck to a person riding a bicycle. A motionless couch seat is struck by a falling, tired, student who comes to rest on the couch.

A canon on rollers fires a canon ball and rolls backward. Which of the following are true statements?

The speed of the canon ball is greater than the canon's speed. The momentums of the canon and canon ball are equal.

When a fullback hits a defensive back, which of the following are true?

The total momentum before and after the collision are the same. The force on the fullback is the same magnitude but in the opposite direction as the force on the defensive back.

Two identical steel balls move straight towards each other at the same speed. What happens when they elastically collide with each other?

They both bounce straight back with the same initial speed.

In which of the following situations is the total momentum always conserved?

When the net force on the system is zero. When all the forces on the system are internal to the system.

When a ball bounces against a wall there will be large change in velocity in short period of time. This means the is large, hence the net must be proportionately large as well.

acceleration force

To increase the impulse on an object someone could

apply the force for a longer time increase the applied force

Sometimes interactions are difficult to analyze during the process that causes changes in motion. In these cases it can be easier to describe the overall in motion rather than detail it step by step. [insert one word in the blank]

change

When two objects collide inelastically, the energy can be lost by

deformations of the object(s). sound generation. heat generation.

A puck slides along a frictionless surface in the northward direction. An eastward impulse is applied to the puck. The change in momentum of the puck is in the direction.

eastward

When a rocket exhausts some gas during propulsion, the momentum of the exhaust gas must equal the momentum of the rocket. This is because they exert and forces due to Newton's third law.

equal opposite

True or false: If an Westward moving object experiences an impulse towards the East, it must now be moving Eastward.

false

A car airbag will increase the time of a collision compared to a collision where the person hits the steering wheel. In both cases (airbag and steering wheel) the person comes to rest. The advantage of the airbag is that the on the person by the airbag is less than the steering wheel would generate, and thus less injury will occur. [insert one word in the blank]

force

Which of the following quantities are vectors?

force Δvelocity impulse

The net force acting on an object multiplied by the time that force acts is called the .

impulse

When a marble launcher shoots a marble, the recoil velocity of the launcher can be reduced by the mass of the launcher.

increasing

A piece of al dente pasta is thrown against the wall to see if it is cooked. Being cooked, the noodle sticks to the wall after its perfectly collision.

inelastic

When catching a ball people tend to move their hands backwards with the ball a little bit. Doing so increases the time the hand exerts a stopping force on the ball, which means overall force needs to be applied.

less

In real-world collisions, the net force is rarely exactly zero; however, conservation of may still be used since the external forces on the system are much smaller than the forces involved in the collision.

momentum

The amount of motion, that is, how much motion an object has, is called the object's . (fill in the blank with one word.)

momentum

When an impulse acts on an object, it produces a change in the object's

momentum

Two objects collide, one moving quickly to the and the other at rest. After the collision, the two objects stick together and the whole system moves to the right, since the net external force was zero.

right

The impulse-momentum principle relates the force multiplied by the time of the interaction (the impulse) with the change in the momentum of an object. This comes from a rearrangement of Newton's law. It is thus not a new law, but a new way of looking at a known law.

second

When a fist hits a punching bag, the forces on both have the same but opposite directions. Thus, the impulse and change in momentum are also equal in magnitude and in direction for each object.

size opposite

In order for two objects to collide perfectly inelastically, they must together after the collision.

stick

When a bat strikes a ball, which of the following are the same on both the bat and the ball?

the magnitude of the force the magnitude of the impulse the time the force acts

The impulse on an object is the multiplication of the _____ multiplied by the _____.

time interval net force

A ball thrown upward at 20 m/s will have a momentum in the direction.

upwards

A dropped tennis ball bounces back upwards after striking the floor. The velocity thus went from downwards to upwards. The net force to cause this change in velocity must be upwards. The impulse must therefore be in direction.

upwards

Rank the following forces and time intervals in order, from the largest impulse (top) to the smallest impulse (bottom). Remember that impulse is a vector. A positive vector is considered greater than a negative vector.

50 150 250 10 -50 -150

A car traveling at 20 m/s eastward will have a momentum in the direction.

eastward

If the net external force on a system of objects is zero, then the total is conserved.

momentum

The amount of motion (or quantity of motion) of an object is its

momentum

The momentum of an object depends on its

velocity. mass.

If a system contains only two objects, such as two stars, that exert a force on each other, then the net force on the system must be since the system contains both the action and reaction forces.

zero