Physics for allied health Exam 1 Review

A .30-06 rifle fires a bullet with a mass of 10 g at a velocity of 800 m / s . If the rifle has a mass of 4 kg , what is its recoil speed ? m1v1=m2v2

2 m/s

A baseball is hit with a horizontal speed of 45 m / s and a vertical speed of 18 m / s upward . What are these speeds 1 s later

2 m/s downward

How does padding dashboards in automobiles make them safer ? Explain your answer in terms of impulse and momentum .

Padded dashboards lengthen the collision time and reduces the force felt.

The moons speed in its orbit is approximately 1 km/s, and the earth-moon distance is 380,000 km. Show that these numbers yield an acceleration for the moon that is very close to that given in the text.

0.00263 m/s^2

A fox is chasing a bunny . The bunny is initially hopping east at 1 m / s when it first sees the fox .Over the next half second , the bunny changes its velocity to west at 4 m / s and escapes. What was the bunny's average acceleration ( magnitude and direction ) during this 2 second interval ?

10 m/s^2 west

The gravitational force between two very large metal spheres in outer space is 50 N. How large would this force be if the mass of each sphere were cut in half ?

12.5 N

Which produces the larger impulse : a force of 3 newtons acting for 3 seconds or a force of 4 newtons acting for 2 seconds ? Explain . Impulse= F•t

3 N acting for 3 seconds produces a larger impulse because it produces 9 N and the other produces 8N

If a baseball is hit with a vertical speed of 30 m / s and a horizontal speed of 6 m / s , how long will the ball remain in the air ? How far from home plate will it land ?

36 m

The acceleration due to gravity on Titan , Saturn's largest moon , is about 1.4 m / s² . What would a 50 - kg scientific instrument weigh on Titan ?

70 N

Give examples from everyday life in which an object's accel eration is pointed downward and the object is ( a ) speeding up and ( b ) slowing down .

A) elevator starting up, astronaut shuttle taking off B) elevator slowing down as it reaches the ground floor, bungee jumper slowing down as it reaches bungee limit

What is the change in velocity for each of the following initial and final velocities ? a . 75 km / h right to 100 km / h right b . 75 km / h right to 100 km / h left

A. 25 km/h right B. 175 km/h left

How do the acceleration vectors differ on opposite sides of the path for uniform circular motion ? How are they the same ?

Acceleration vectors point in the opposite direction. Both vectors point at the center.

A 4 - kg ball traveling to the right with a speed of 4 m / s collides with a 5 - kg ball traveling to the left with a speed of 2 m / s . What is the total momentum of the two balls before they collide ? After they collide ? P=m•v

Before colliding: 4kg ball - 16 kg • m/s right 5 kg ball - 10 kg • m/s left After colliding : 6 kg • m/s right

The following strobe drawings represent the motions of two cars , a and b . During which interval of the motion of car a is the average speed of car a approximately equal to the average speed of car b ?

Between B+C for car A. The same distance between B+C as all strobe markings for car B.

The following figure shows a racetrack with identical cars at points A , B , and C. The cars are moving clockwise at constant speeds . Draw arrows indicating the direction of the net force on each car and the instantaneous velocity of each car In what direction would car A travel if there were an oil slick at its position ? Why ?

Car A would travel in the direction of tis velocity because no net force would be acting on it.

You kick a soccer ball 15 meters without hurting your foot much . You then pump the ball up until it is really hard ( the extra air does not significantly change the ball's mass ) and again kick it 15 meters . This time it hurts a lot . Using the concept of impulse , explain why it hurts more in the second case .

Change in momentum and impulse is the same both times. When the ball is pumped up the time of impact is reduced which increases the average force.

Most footraces take place on unbanked tracks. How do the racers turn the corners?

Friction between the runners shoes and the ground (centripetal force)

A soft rubber ball ( m = 0.5 kg ) was falling vertically at 6 m / s just before it hit the ground and stopped . What was the impulse experienced by the ball ? If the ball had bounced , would the impulse have been less than , equal to , or greater than what you calculated ?

If the ball bounced it would have had a greater change in momentum and therefore requiring a greater impulse.

Two objects with the same speed , one moving north and the other moving east , collide and stick together. If the northbound object has twice the mass of the eastbound object , which of the indicated paths in the following figure represents the most likely final motion of the pair ? Justify your answer using the concept of linear momentum . P=m•v

If the mass of the northbound object is 2X mass of the eastbound object the final momentum will be more north than east. (B)

A 2 - kilogram cart moving at 6 meters per second hits a stationary 2 - kilogram cart . The two move off together at 3 meters per second . Lee contends , " Momentum is conserved in this collision because the momentum of the system has the same value before and after the collision Jackie counters , " The momentum of the system before the collision is 12 kilogram - meters per second , not zero , so momentum is not conserved . " With which student do you agree , and why ?

Lee is correct because its the change of momentum thats important not the value of a soecific time.

Under what conditions is mass conserved ?

Mass is conserved if the system is closed; nothing can enter or leave and mass' numerical value stays the same.

Two identical objects , one moving twice as fast as the other , collide with each other as shown in the following figure . If the two objects stick together after the collision , will they be moving to the left , to the right , or not at all ? Justify your answer using the concept of linear momentum .

Momentum after collisions is to the right.

A student who recrntly studied thr law of conservation of linesr momentum decides fo propel a go-cart by having a fan blow on a board as shown in thr following figure. This idea wont work very well. Why not?

Momentum tranferred by the fan to the air molecules is neglected by the air molecules hitting the screen.

An ancient marathoner covered the first 20 miles of the race in 4 hours . Can you determine how fast he was running when he passed the 10 - mile marker ?

No we can only calculate average speed from the information given. We cant calculate instantaneous speed at mile marker ID.

Does a defensive end with a mass of 120 kg running at 6 m / s have a larger or smaller momentum than a running back with a mass of 100 kg running at 8 m / s ?

Running back has more momentum

An astronaut in the space shuttle pushes off a wall to float across the room . What effect ( if any ) does this have on the motion of the shuttle ?

Shuttle experiences an impulse in the opposite dirrection; increasing its momentum in that direction.

During the Gulf War with Iraq in 1991 , a newspaper story reported that American spy satellites were in stationary orbits over Iraq , providing continuous intelligence information . Explain why this is impossible .

Stationary orbits (geosynchronous) need to be situated over the equator. Iraq is too far north about the equator.

If an apple were placed in orbit at the same distance from the earth as the moon, what acceleration would the Apple have?

The Apple would have the same acceleration as the moon; acceleration is not dependent on the mass.

Is the size of the gravitational force that Earth exerts on the apple in orbit smaller than , larger than , or the same size as the force the apple exerts on Earth ? Why ?

The force is the same- newtons 3rd law (equal but opposite direction)

What is the force that allows a person on in line skates to turn a corner ? What happens if this force is not strong enough ?

The force of friction (centripetal force). The skater would slide off and in the direction of his velocity.

Comment on the following statement made by a TV newscaster during an Apollo flight to the Moon: "The spacecraft has now left the gravitational force of Earth."

The force of gravity extends to infinity; spacecraft never leaves gravitational force of the earth.

You have no doubt seen pictures of the astronauts floating around inside a space shuttle as it orbits some 300 kilometers above Earth's surface . Would the force of gravity Earth exerts on an astronaut be the same as , a little less than, or much less than the force that the astronaut would experience on Earth's surface ? Why ?

The force of gravity is only slightly less because the 300 km distance above the earths surface is so small compared to the earths 6400 km radius.

A 2 - kilogram rubber ball falls off a counter and lands on the floor . Just before hitting the floor , the ball has a speed of 4 meters per second . If the ball bounces , is the magnitude of the impulse the floor exerts on the ball less than , equal to , or greater than 8 kilogram - meters per second ? Why ?

The original momentum hust before hitting the floor is 8 kg • m/s (p=mv) downward and since the ball comes off the floor the final momentum is directed upward and must be > 8 kg • m/s.

Which ( if either ) has the greater average speed : a car that travels from milepost 35 to milepost 40 in 5 minutes , or one that travels from milepost 68 to milepost 78 in 10 minutes ?

The speeds are the same

What force if any causes the planets to execute (nearly) circular orbits?

The sun's gravitational force keeps the planets in their nearly circular orbits.

The Sun has a profound influence on Earth's motion . Does Earth influence the Sun's motion ? Explain.

The suns force on earth is equal and opposite of the earths force on the sun (newtons 3rd law) but because the sun is so much more massive that the earth the force on the sun in much less.

As a satellite orbits earth, the gravitational force is constantly pulling the satellite inward. What counters this force?

There's no countering force. The satellite falls towards the earth but it moves so fast sideways it never gets any closer.

Two balls , one of mass 1 kilogram grams , roll off the edge of a table at the same time travel and one of mass 4 kilo ing at the same speed . Which ball hits the floor first Why

They both hit at the same time because free fall acceleration (10 m/s^2) is independent of mass.

You are steaming across the Atlantic Ocean on a large cruise ship . What happens to your weight as the ship leaves the deep waters of the North Atlantic and enters the shallow coastal waters of the United States ?

Your weight is slightly more because of the increasing density below you as you move from deep water (< dense) to shallow water/ land (> dense).