Physics 1310- Hw #3

A motorboat that normally travels at 8 km/h in still water heads directly across a 6-km/h flowing river. The resulting speed of the boat is about

10 km/h.

What is the acceleration of a car moving along a straight road that increases its speed from 0 to 100 km/h in 10 s?

10 km/h·s

If a freely falling object were equipped with a speedometer, its speed reading would increase each second by about

10 m/s.

If you throw a ball straight downward (in the absence of air resistance), after leaving your hand its acceleration is

10 m/s2.

Neglecting air resistance, a bullet fired straight down from the top of a high cliff has an acceleration of

10 m/s2.

When a ball thrown straight upwards reaches the very top of its path, its acceleration is

10 m/s2.

A river 100 m wide flows due south at 1 m/s. A boat that travels 1 m/s relative to the water is pointed due east as it crosses from the west bank. The boat reaches the east bank

100 m farther south.

A ball is thrown upwards and returns to the same location. Compared with its initial speed its speed when it returns is about

the same.

A rock dropped from a 5-m height accelerates at 10 m/s2 and strikes the ground 1 s later. If the rock is dropped from a height of 2.5 m, its acceleration of fall is

the same.

A ball rolling down an inclined plane each second picks up ______.

the same amount of speed each second

An object covers a distance of 8 meters in the first second of travel, another 8 meters during the next second, and 8 meters again during the third second. Its acceleration is

0 m/s2.

A cart changes its speed from 90 m/s to 100 m/s in 10 seconds. During this interval its acceleration is

1 m/s2.

When you walk at an average speed of 4 m/s, in 5 s you'll cover a distance of

20 m.

An object at rest near the surface of a distant planet starts to fall freely. If the acceleration there is twice that of the Earth, its speed one second later would be

20 m/s.

If a freely falling object were equipped with a speedometer on a planet where the acceleration due to gravity is 20 m/s2, then its speed reading would increase each second by

20 m/s.

An object falls freely from rest on a planet where the acceleration due to gravity is twice as much as on Earth. In the first 5 seconds it falls a distance of

250 m.

Ten seconds after starting from rest, a car is moving at 40 m/s. What is the car's acceleration?

4.0 m/s2

At one instant a heavy object in air is moving upward at 50 m/s. One second later its speed is approximately

40 m/s.

A ball starting from rest at the top of an inclined plane accelerates at 2 m/s2 and reaches the bottom of the plane in 3 seconds. What is the length of the plane?

9 m

What is the speed over the ground of an airplane flying at 100 km/h relative to the air caught in a 100-km/h right-angle crosswind?

141 km/h

Phil leans over the edge of a cliff and throws a rock upward at 5 m/s. Neglecting air resistance, two seconds later the rock's speed is

15 m/s.

The time it takes a car to attain a speed of 30 m/s when accelerating from rest at 2 m/s2 is

15 s.

If a stone falls to the bottom of a mineshaft in 6 seconds, then the depth of the shaft is about

180 m.

A ball starting from rest at the top of an inclined plane gains a speed of 2 m/s for each second it rolls. What is its acceleration down the incline?

2 m/s2

The total time it takes a projectile fired straight up at 10 m/s to reach the top of its path and return to its starting point is about

2 s.

The average speed of a horse that gallops 10 kilometers in 30 minutes is

20 km/h.

What is the average speed in kilometers per hour of a horse that gallops a distance of 15 km in a time of 30 min?

30 km/h

A ball freely falling at 20 m/s will in the next second have a speed of ______.

30 m/s

What is the acceleration of a car that starts from rest and 5 seconds later reaches a speed of 20 m/s?

4 m/s2

A humming bird flying at 4 km/h that gets caught in a 3-km/h crosswind has a resultant speed of about

5 km/h.

One half second after starting from rest, a freely falling object will have a speed of about

5 m/s.

Phil leans over the edge of a cliff and throws a rock upward at 5 m/s. Neglecting air resistance, one second later the rock's speed is

5 m/s.

A car's speed 3 seconds after accelerating from rest at 2 m/s2 is

6 m/s.

Jogging Jake runs at 4 m/s along a train flatcar that moves at 10 m/s in the opposite direction. Jake's speed relative to the ground is

6 m/s.

If a car increases its velocity from zero to 60 m/s in 10 seconds, its acceleration is

6 m/s2.

At one instant an object in free fall is moving downward at 50 m/s. One second later its speed is

60 m/s.

What is the effect of air resistance on the acceleration of falling objects?

Air resistance decreases the acceleration of falling objects.

What exactly is meant by a "freely falling" object?

An object in free fall falls under gravity alone with no friction.

Which BEST describes what occurs when a body accelerates?

Change in velocity per unit time

What is the distance fallen for a freely falling object 1 s after being dropped from a rest position? What is the distance for a 4-s drop?

It falls 5 m in 1 s and 80 m in 4 s.

What is the gain in speed per second for a freely falling object?

It gains 10 m/s2.

When an object is thrown upward, how much speed does it lose each second (ignoring air resistance)?

It loses 10 m/s of speed each second until it reaches the high point, then it gains 10 m/s each second.

If a car is moving at 90 km/h and it rounds a corner, also at 90 km/h, does it maintain a constant speed? A constant velocity?

It maintains a constant speed, but does not maintain a constant velocity.

As you read this in your chair, how fast are you moving relative to the chair? Relative to the Sun?

You are not moving relative to the chair, but you are moving over 100,000 km/h relative to the Sun.

Galileo discovered that when air resistance can be neglected, all objects fall with the same ______.

acceleration

A freely-falling watermelon falls with constant

acceleration.

A vehicle undergoes acceleration when it

all of the above

If an object moves with constant acceleration, its velocity must

change by the same amount each second.

A ball tossed vertically upward rises, reaches its highest point, and then falls back to its starting point. During this time the acceleration of the ball is always

directed downward.

If an object falling freely were somehow equipped with an odometer to measure the distance it travels, then the amount of distance it travels each succeeding second would be

greater than the second before.

Phil Physiker standing at the edge of a cliff throws one ball straight up and another ball straight down, both with the same speed. Neglecting air resistance, which ball hits the ground below with the greater speed?

neither, both hit with the same speed

The distance a freely falling object falls from rest in one-half second is

none of the above

While a car travels around a circular track at a constant speed, its

none of the above

The accelerations possible for a ball on an inclined plane

range from zero to g.

While an iron block near the Earth's surface is in free fall, it undergoes an increase in

speed.

A cart maintains a constant velocity of 100 m/s for 10 seconds. During this interval its acceleration is

zero.