chap 10

A gun with a muzzle velocity of 100 m/s is fired horizontally from a tower. Neglecting air resistance, how far downrange will the bullet be 1 second later?

100 m

Escape speed from Earth is

11.2 km/s

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

It stays constant.

Who envisioned the motion of planets as projectiles obeying the laws of physics?

Newton

Our Moon in Earth orbit travels fastest when it is

closest

According to Kepler, the line from the Sun to any planet sweeps out equal areas of space

in equal time intervals.

As soon as a ball rolls off the edge of a table

it is not acted on by any horizontal forces

A lunar month is about 28 days. If the Moon were closer to Earth than it is now, the lunar month would be

less than 28 days.

Minimal orbital speed about Earth is about 8 km/s, and about the Moon is

less than 8 km/s.

An object is thrown vertically into the air. In this case air resistance affects motion. Compared with its time for ascent, the time for its descent is

longer

Compared with the period of satellites in close Earth orbit, the period of satellites orbiting far from Earth is

longer.

Does the mass of the ball make a difference?

no

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

11.2 km/s

A projectile is launched upward at an angle of 70° from the horizontal and strikes the ground a certain distance downrange. For what other angle of launch at the same speed would this projectile land just as far away?

20°

It there were no gravity a stone thrown upward at 45 degrees would follow a straight-line path. But because of gravity, at the end of 1 second, the stone is actually

5 m below the straight line.

A projectile is launched at 30° above ground level. What other angle at the same speed will result in the same range?

60°

Rank their orbital speed from greatest to least

A, B, C

What exactly is a projectile?

An object that is projected by some means and continues in motion by its own inertia.

Rank their time to orbit Earth speed from greatest to least.

C,B,A

When air resistance is neglected, why does the vertical component of velocity for a projectile change with time, whereas the horizontal component of velocity doesn't change?

Gravity is a purely vertical force.

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

A stone is thrown upward at an angle. What happens to the magnitude of the vertical component of its velocity as it rises? As it falls?

It decreases while rising, but it increases while falling

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

It first decreases to zero and then increases in the opposite direction

A stone is thrown upward at an angle. What happens to the horizontal component of its velocity as it rises? As it falls?

Rising or falling, it does not change

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

The ball thrown horizontally

Consider the video demonstration that you just watched. A more complete explanation of what you saw will be possible after covering Newton's laws. For now, consider the following question: How would the result of this experiment change if we replaced the ball with another one that had half the mass? Ignore air resistance.

The ball would still land in the cart.

Why doesn't the force of gravity change the speed of a bowling ball as it rolls along a bowling lane?

The force is at a right angle to the motion.

How can a projectile "fall around the Earth"?

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

When Kepler devised his laws of planetary motion, he was most influenced by

Tycho Brahe.

A dropped ball gains speed because

a gravitational force acts on it.

Project a cannonball from atop Newton's hypothetical mountain at 8 km/s and it orbits Earth. Project it at 9 km/s and the shape of the orbit is

an ellipse

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

The conservation of energy applies to satellites in

circular orbit. elliptical orbit.

How far does the bullet drop from a straight-line horizontal path by the time it reaches the target?

d = 2.76 m

A satellite in an elliptical orbit about a planet travels much faster when it is directly over a

none of the above

As soon as a bowling ball rolls off the edge of a table its horizontal component of velocity

remains constant.

The hang time of a basketball player who jumps a vertical distance of 2 feet (0.6 m) is about 2/3 second. What will be the hang time if the player reaches the same height while jumping 4 feet (1.2 m) horizontally?

t = 2/3 s

Dr. Chuck projects a ball horizontally from a lab bench. The ball lands on a bullseye marked on the floor a horizontal distance away. Compared to the time for the ball to simply drop vertically from the bench, the time in the air for Dr. Chuck's projected ball is

the same.

Hang time is the time your feet are off the ground in a jump. If you jump upward inside a moving vehicle, your hang time will be

the same.

The orbital path of a satellite has two focal points. When both focal points are together

the satellite path is a circle.

Nellie tosses a ball upward at an angle. Assuming no air resistance, which component of velocity changes with time?

the vertical component

Suppose the height of the net is 1.05 m , and the court's border is 12.2 m from the bottom of the net. Use g =10 m/s2 and find the maximum speed of the horizontally moving ball clearing the net..

v = 27 ms

A horizontally moving tennis ball barely clears the net, a distance y above the surface of the court. To land within the tennis court the ball must not be moving too fast. To remain within the court's border, a horizontal distance d from the bottom of the net, Find the ball's maximum speed over the net.

v = d2yg√

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