Ch 7: Momentum & Impulse

A softer landing occurs when an falling object bounces from a surface

In an extended time

which of the following mathematical expressions should be used to calculate the momentum of an auto?

Mass x Velocity

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

Momentum

One form of the proper metric unit for momentum is

N*sec

A ping - pong ball is dropped vertically onto a stationary bowling ball resting on the floor. Which of the balls experiences the greater force as a result of the collision?

Neither, both experience forces of the same size

A car moving east collides with a truck moving north. The vehicles have the same speed but the truck has twice the mass of the car. If the vehicles stick together after the collision, what is the path followed by the vehicles after the collision?

Path B

Suppose you are out on a frozen lake, where there is no friction. Which of the following would start you moving towards the shore?

Removing a shoe and throwing it away from the shore

A 5-kg shark swimming at 1 m/s swallows an absent-minded 1-kg fish swimming toward it at 4 m/s. The speed of the shark after his meal is

Shark 1: m= 5 kg v= 1 Shark 2: m= 1 kg v= 4 both go toward each other → subtract m1(v1) + m2(v2) 5(1) - 1(4) 5 - 4 = 1 v = 1/6 m/s

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

Collisions between which pairs of objects is likely to be most nearly elastic?

Two steel balls

Two billiard balls having the same mass and speed roll toward each other. What is their combined momentum after they meet?

Zero

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

both the same

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

both the same

You're driving down the highway and a bug spatters into your windshield. Which undergoes the greater change in momentum during the time of contact?

both the same

A cannon recoils while firing a cannonball. The speed of the cannon's recoil is relatively small because the

cannon has much more mass than the cannonball.

The purpose of an air bag in an auto is to

decrease the force applied to you during a collision

A 5-kg fish swimming at 1 m/s swallows an absent-minded 1-kg fish at rest. The speed of the larger fish after lunch is

fish 1: m= 5 kg v= 1 fish 2: m= 1 kg v= 0 m1(v1) + m2(v2) 5(1) + 1(0) 5 + 1 = 6 kg v= 5/6 m/s

The total momentum of a flock of identical birds could be zero only if the birds are

flying in different directions

Force F, acting for time T and over a distance D, gives impulse I. To get the same impulse using half the force, it would be necessary for the force to act

for a time 2T

A box is pushed eastward across a rough horizontal floor by a force acting parallel to the floor. A force providing an impulse directed westward on the body is

friction

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

greater

When a boxer moves into an oncoming punch, the force experienced is

increased

The momentum of a truck is increased by a factor of 2; its weight does not change. Thus,

its speed doubled

Padded dashboards in cars are safer in an accident than non-padded ones because passengers

lengthened time of contact.

A large heavy truck and a small baby carriage roll down a hill. Neglecting friction, at the bottom of the hill, the baby carriage will likely have

less momentum

An 80-kg football player travels to the right at 8 m/s and a 120-kg player on the opposite team travels to the left at 4.0 m/s. The total momentum is

m1(v1) + m2(v2) Opposite turns the plus to subtraction. 80(8) - 120(4.0) 60 - 480 = 160 kg m/s to the right

A tiny gun made of a strong but very light material fires a bullet more massive than the gun itself. For such a weapon

the target would be safer than the shooter.

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 contact is increased

When a boxer is moving away from a punch, the force experienced is reduced because

time of contact is increased

A quantity which is conserved in the collision of a car and a truck is

total momentum

A freight train rolls along a track with considerable momentum. if it rolls at the same speed but has twice as much mass, its momentum is

twice

A piece of putty moving with 1 unit of momentum strikes and sticks to a heavy bowling ball that is initially at rest. Both move with a combined momentum of

1 unit

The speed of a 4-kg ball with a momentum of 12 kg m/s is

12 = 4*V → 12/4 = 3 [momentum (p) = mass (m) x velocity (v)]

A child runs at 3.0 m/s and jumps onto a sled, initially at rest. If the child's mass is 36 kg,and if the child and sled slide off together at 2.0 m/s after the collision, the sled's mass

18 Kg

A bullet of mass 0.010 kg and speed of 200 m/s is brought to rest in a wooden block after penetrating a distance of 0.10 m. This process takes 0.02 second. The magnitude of the impulse delivered to the bullet by the block during this time

2.0 Ns

A 30-kg child runs at 3.0 m/s and jumps onto a shopping cart and holds on for dear life.The cart has a mass of 20 kg. Assuming the child rides on the cart after the collision, the speed of the child and shopping cart just after the child jumps on is

2.0 m/s

In a head-on automobile collision, a person's momentum could be reduced from 2000 kg m/s to zero in just 0.1 s. If this occurs, the average force exerted to stop the person is

20,000 N

The average braking force of a 1000-kg car moving at 10 m/s braking to a stop in 5 s is

2000 N

If the speed of a car is tripled, the impulse required to stop the car changes by a factor of

3

The average force required to accelerate a 0.20-kg ball from rest to 30 m/s in 0.002 s is

3000 N

Moving at a constant speed, an elevator lifts a 1000 N package 10 meters in 3 seconds.During this time, the impulse delivered to the package by the elevator floor is

3000 Ns up

3 kg block, initially moving due east at 6 m/s, is acted upon by an impulse having magnitude 6 Ns and direction due west. The final velocity of the block is

4 m/s east

The mass of a ball moving at 3 m/s with a momentum of 48 kg m/s is

48 = m*3 → 48/3 = 16 [momentum (p) = mass (m) x velocity (v)]

A fire fighting vehicle of mass 12,000 kg is at rest but free to roll with no resistance. If you push it forward with a force of 500 N, the momentum at the end of 10 s of pushing will be

5000 kg m/s

The change in momentum that occurs when a 1.0 kg ball traveling at 4.0 m/s strikes a wall and bounces back at 2.0 m/s is

6 kg m/s

It is correct to say that impulse is equal to

A corresponding change in momentum

A racquetball is dropped from a height of one meter. It bounces off the floor and rises to a height of 0.8 m. The collision with the floor was

A partially inelastic collision

Which of the following has the largest momentum relative to Earth's surface?

A pickup truck speeding along a highway

In attempting to pull a 1500-kg car out of a ditch, Arnold exerts a force of 300 N for three seconds, Bob exerts a force of 500 N for two seconds, and Cecil exerts a force of 200 N for four seconds. Who provided the greatest impulse?

Bob

When bullets are fired from an airplane in the forward direction, the momentum of the airplane is

Decreased