PHYS 1415 Chapter 4

A bullet fired horizontally hits the ground in 0.5 s. If it had been fired with twice the velocity it would have hit the ground in

0.5 s

A woman who normally weighs 400 N stands on top of a very tall ladder so she is one Earth-radius above Earth's surface. What is her weight there?

100 N

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 s later?

100 m

A ball is thrown horizontally from the top of a tall cliff. Three seconds later, the ball has fallen a vertical distance of

45 m

A stone is thrown horizontally from the top of a cliff. One second after leaving your hand it drops a vertical distance of

5 m

For each 8-km segment of a satellite in close Earth orbit, the "drop" toward Earth is about

5 m

A projectile is launched straight upward at 50 m/s. Neglecting air resistance its speed upon returning to its starting point is

50 m/s

Phil stands at rest with both feet on a scale that reads 500 N. After he gently lifts one foot, the scale reads

500 N

A projectile is launched at an angle of 15° above the horizontal and lands downrange. With no air resistance, what other projection angle for the same speed would produce the same downrange distance?

75 degrees

If the sun were twice as massive

It's pull on Earth would double and the pull of Earth on the Sun would double

A dropped ball gains speed because

a gravitational force acts on it

Escape speed for a rocket is less from a) the Moon b) Earth c) the Sun d) same for each

a) the Moon

A satellite near Earth makes a full circle in about 90 minutes. Much farther from Earth, say at the distance to the Moon, time for a full circle would be

about 28 days

A bullet fired from a rifle begins to fall

as soon as it leaves the barrel

Earth satellites are typically more than 100-km high so as to mainly be above the Earth's

atmosphere

To drop a package to Earth from a satellite, project it

behind a satellite speed

An airplane flies at 40 m/s at an altitude of 50 m. The pilot drops a heavy package that falls to the ground below. Neglecting air resistance, the package will land

beneath the plane

Acceleration is greater for a satellite in elliptical orbit when it is

closest to Earth

You can experience weight

in a rotating habitat in space, standing on Earth's surface, and in an accelerating elevator away from earth

Two objects move toward each other due to gravity. As the objects get closer and closer, the acceleration of each

increases

Two objects move toward each other due to gravity. As the objects get closer and closer, the force between them

increases

When the distance between a pair of stars decreases by half, the force between them

increases to four times as much

The Moon continually falls toward Earth, but doesn't get closer because

its tangential velocity causes it to fall around as well as toward Earth

An object is thrown vertically into the air. Because of air resistance, the time for its descent will be

longer than the ascent time

From Earth, one satellite appears to overtake another. The faster satellite that is seen to overtake the other is

lower

For the astronauts inside an orbiting space vehicle the force of gravity that acts on them is

mainly due to Earth below

Each of us weighs slightly less inside the ground floor of a skyscraper than we do on the ground away from the skyscraper because the

mass of the building attracts us slightly upward

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

more than 28 days

At some point between Earth and the Moon, the forces due to gravity on a space traveler would be the same when this point is

nearer to the Moon

An Earth satellite in an elliptical orbit travels fastest when it is

nearest Earth

With no air resistance a projectile fired horizontally maintains its horizontal component of velocity because

no horizontal force acts on it

What holds Earth satellites up so they don't crash into Earth?

nothing, they continually fall fast enough around Earth not to crash

A projectile that is fired vertically at 8 km/s from Earth's surface will

rise and fall back to Earth's surface

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

the vertical component

Without air resistance, a projectile fired horizontally at 8 km/s from a mountain top will

trace a curve that matches Earth's curvature, return to its starting position and repeat its falling behavior, and accelerate downward at g as it moves horizontally

Consider two planets in space that gravitationally attract each other. If the mass of one planet is doubled, and the distance between them doesn't change, then the force between them is

twice as much

Inside a freely-falling elevator your

weight is zero

An airplane flying overhead drops a care package directly over Mike at rest in his Corvette. Neglecting air resistance, the package will land

well ahead of Mike and his corvette

If a projectile is fired straight up at a speed of 10 m/s, neglecting air resistance, the total time to return to its starting position is

2 s

If there were no gravity, a ball thrown upward at an angle would follow a straight-line path. Due to gravity, however, at the end of 2 s it is

20 m below the straight line

A softball player determines her pitching speed by throwing a ball horizontally from an elevation of 5 m above the ground. The ball lands 20 m downrange. What is her pitching speed?

20 m/s

Ignoring air resistance, what maximum speed can be given to a horizontally moving tennis ball as it clears the net 1.25 m high to remain within the edge of the court, which is 12.0 m from the bottom of the net?

24 m/s

A softball player determines her pitching speed by throwing a ball horizontally from an elevation of 20 m above the ground. The ball lands 50 m downrange. What is her pitching speed?

25 m/s

According to Newton, the greater the masses of interacting objects, the a) less gravitational force between them b) greater the force between them by the square of the distance c) greater the force between them by the square of the masses d) greater the gravitational force between them

d) greater the gravitational force between them

If Earth's mass somehow decreased with no change in its radius, your weight would

decrease also

If your mass doubles, your weight

doubles

If the masses of two planets doubles and the distance between them reduces by half, the force between them would be a) unchanged b) twice as much c) half as much d) four times as much e) none of the above

e) none of the above

Your weight is equal to mg when you are

firmly supported on a horizontal surface and in equilibrium

An Earth satellite is simply a projectile

freely falling around the earth

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

greater