Physics Test 2 Chapter 10

How can a projectile "fall around the Earth"?

1. A projectile can "fall around Earth" if the distance it falls matches the curvature of Earth. 2. In a circular orbit around a spherical planet, the force and the fall are always toward the center. 3. The projectile falls 5 m for every 8 km and so does Earth.

What is the ratio of escape speed from Earth to circular orbital speed? Ignore air resistance.

1.41

You're in an airplane that flies horizontally with speed 1200 km/h (320 m/s ) when an engine falls off. Neglecting air resistance, assume it takes 35 s for the engine to hit the ground.Find the horizontal distance that the aircraft engine falls.

11 km

Escape speed from Earth is any speed equal to or greater than __________

11.2 km/s

Maximum range occurs for ideal launch at what?

45

A projectile falls beneath the straight-line path it would follow if there were no gravity. How many meters does it fall below this line if it has been traveling for 1 s? For 2 s?

5 m, 20 m

Same range is obtained from two different launching angles when the angles add up to what?

90

Why do the two objects hit the table at the relative times that they do?

Gravity pulls the same amount on both, and they both drop the same distance.

At what part of an elliptical orbit does an Earth satellite have the greatest speed? The lowest speed?

Greatest nearest Earth; lowest furthest from Earth

What parts a parabolic trajectory change and do not change?

Horizontal component remains unchanged through trajectory, only vertical component changes

Past the apogee, satellite moves in the same direction as the force component and speed and KE increase. what happens next?

Increase continues until past the perigee and cycle repeats.

Predict how the vertical component of the velocity will change with time after the projectile is fired.

It first decreases to zero then increases in the opposite direction

Predict how the horizontal component of the velocity will change with time after the projectile is fired.

It stays constant

For an Earth satellite in circular orbit, list all the values that do not change.

Only speed, gravitational force, and distance from Earth

apogee

PE is greatest when the satellite is farthest away

Why doesn't the force of gravity change the speed of a satellite in circular orbit?

The force is at a right angle to the velocity.

Why is kinetic energy a constant for a satellite in a circular orbit but not for a satellite in an elliptical orbit?

The force of gravity is perpendicular to the motion in a circular orbit but not in an elliptical orbit.

What is Kepler's second law of planetary motion?

The line from the Sun to any planet sweeps out equal areas of space in equal time intervals.

What is Kepler's first law of planetary motion?

The path of each planet around the Sun is an ellipse with the Sun at one focus.

What is Kepler's third law of planetary motion?

The square of the orbital period of a planet is directly proportional to the cube of the average distance of the planet from the Sun (for all planets)

When Dr. Hewitt releases the two objects, how can we tell whether one of the objects hits the ground first or whether they both hit at the same time?

We are able to hear the two balls fall.

A ball is thrown horizontally from a cliff at a speed of 10 m/s . You predict that its speed 1 s later will be slightly greater than 14 m/s . Your friend says it will be 10 m/s. Who is correct?

You

When satellite gains altitude and moves against gravitational force what happens?

its speed and KE decrease and decrease continues to the apogee.

With air resistance, the maximum range occurs for a baseball batted at what?

less than 45° above the horizontal (~25° −34°

In order to appear motionless to an observer at a fixed location on Earth's surface, the satellite must rotate around Earth at the same ----------- both the location and satellite must be in the ---------------.

rate as Earth rotates around its own axis and both the location and satellite must be in the same line between Earth's center and the satellite.

This can only occur above Earth's equator. Above any other location, the "ring" of satellite motion and the "ring" of motion of the location on Earth's surface -------- be in the same plane.

would not

Vertical positions do what with time?

Become farther apart

You're in an airplane that flies horizontally with speed 1200 km/h (320 m/s ) when an engine falls off. Neglecting air resistance, assume it takes 35 s for the engine to hit the ground. Find the height of the plane?

6.1 km

When Dr. Hewitt releases the two projectiles, which one hits the ground first?

Both balls hit the ground at the same time.

Sum of KE and PE is what during orbit?

Constant at all points in the orbit

Curvature of path is the combination of

horizontal and vertical components of motion

Consider the video you just watched. Suppose we replace the original launcher with one that fires the ball upward at twice the speed. We make no other changes. How far behind the cart will the ball land, compared to the distance in the original experiment?

four times as far...The ball will spend twice as much time in the air (t=2v0y/g, where v0y is the ball's initial upward velocity). When subtracting the horizontal distance the cart travels in time,t, from the horizontal distance the ball travels in time,t, the term involving initial velocity of the cart (which is also the horizontal velocity of the ball) cancels out, leaving only d=12 axt2 (where ax is the cart's horizontal acceleration). The ball will land four times further behind.

You're in an airplane that flies horizontally with speed 1200 km/h (320 m/s ) when an engine falls off. Neglecting air resistance, assume it takes 35 s for the engine to hit the ground.If the airplane somehow continues to fly as if nothing had happened, what is the distance between the engine and the airplane at the moment the engine hits the ground?

6.1 km

Parabola

Curved path of a projectile that undergoes acceleration only in the vertical direction, while moving horizontally at a constant speed

What is the curvature of the Earth?

Earth surface drops a vertical distance of 5 meters for every 8000 meters tangent to the surface

perigee

PE is least when the satellite is closest

How does the speed help a Satellite stay in circular orbit?

Speed • must be great enough to ensure that its falling distance matches Earth's curvature. • is constant—only direction changes. • is unchanged by gravity.

For an Earth satellite in an elliptical orbit, list all the values that do change.

Speed, gravitational force, and distance from Earth

Which ball (if either) has the greatest speed at the moment of impact?

The ball thrown horizontally.. The two balls have the same vertical velocity when they land, but the thrown ball has an additional horizontal velocity component. Since speed is defined as the magnitude of the resultant velocity vector, the thrown ball is moving faster when it lands.

A rocket coasts in an elliptical orbit around Earth. To attain the greatest amount of KE for escape using a given amount of fuel, should it fire its engines to accelerate forward when it is at the apogee or at the perigee? (Hint: Let the formula Fd=ΔKE be your guide to thinking. Suppose the thrust F is brief and of the same duration in either case. Then consider the distance d the rocket would travel during this brief burst at the apogee and at the perigee.)

at the perigee