Linear Motion
What is the hang time of a person who can jump a vertical distance of 0.6 m?
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What vertical distance can a person with a 0.7 s hang time jump?
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A bicycle travels 15 km in 30 minutes. What is its average speed?
.5 km/minute
A pencil lies on your desk. If the Earth is moving around the sun at a speed of 30 km/s, how fast is the pencil moving relative to the desk? How fast is the pencil moving relative to the sun?
0 km/s; 30 km/s
A train travels 6 meters in the first second of travel, 6 meters again during the second second of travel, and 6 meters again during the third second. Its acceleration is
0 m/s^2.
You toss a ball at 5 m/s straight upward. How much time will the ball take to reach the top of its path?
0.5 s
Suppose a car is moving in a straight line and steadily increases its speed. It moves from 35 km/h to 40 km/h the first second and from 40 km/h to 45 km/h the next second. What is the car's acceleration?
5 km/h·s
Suppose a jumper claims a hang time of 2 seconds. Then that jumper must be able to jump a vertical distance of
5 m
An apple falls from a tree and 0.5 second later hits the ground. How fast is the apple falling when it hits the ground?
5 m/s
If a projectile fired beneath the water, straight up, breaks through the surface at a speed of 13 m/s, to what height above the water will it ascend?
8.5 m
T/F? When a car rounds a corner at a constant speed, its acceleration is zero.
False
Speed
a measure of how fast something is moving, always measured in terms of a unit of distance divided by a unit of time, the distance covered per unit time; the rate at which distance is covered
Unit of Velocity
m/s
As an object falls freely in a vacuum, its
velocity increases.
A ball is thrown straight up. At the top of its path its instantaneous speed is
0 m/s.
The vertical height attained by a basketball player who achieves a hang time of a full one second is about
1.2 m
A freely falling object starts from rest. After falling for 1 second, it will have a speed of about
10 m/s
A car accelerates at 2 m/s^2. Assuming the car starts from rest, how much time does it need to accelerate to a speed of 20 m/s?
10 seconds
A stone is dropped from a cliff. After it has fallen 10 m, what is the stone's velocity?
14 m/s
A crate falls from an airplane flying horizontally at an altitude of 1250 m. Neglecting air drag, how long will the crate take to strike the ground?
16 seconds
What is the average speed of a cheetah that runs 88 m in 5 seconds?
17.6 m/s
A jet on an aircraft carrier can be launched from 0 to 40 m/s in 2 seconds. What is the acceleration of the jet?
20 m/s
What speed must you toss a ball straight up so that it takes 4 s to return to you?
20 m/s
If a ball were equipped with a speedometer and allowed to fall freely on a planet where the acceleration due to gravity is 23 m/s^2, the reading on the speedometer would increase each second by
23 m/s
A skateboarder starting from rest accelerates down a ramp at 2 m/s^2 for 2 s. What is the final speed of the skateboarder?
4 m/s
Starting from rest, a car undergoes a constant acceleration of 6 m/s^2. How far will the car travel in the first second?
6 m
A car starts from rest and after 7 seconds it is moving at 42 m/s. What is the car's average acceleration?
6 m/s^2
If a projectile is fired straight up at a speed of 30 m/s, the total time to return to its starting point is about
6 seconds.
Suppose you take a trip that covers 180 km and takes 3 hours to make. Your average speed is
60 km/h.
A freely falling object starts from rest. After falling for 6 seconds, it will have a speed of about
60 m/s
How much time does a car with an acceleration of 5 m/s^2 take to go from 5 m/s to 40 m/s?
7 s
What is the average acceleration of a car that goes from rest to 60 km/h in 8 seconds?
7.5 km/h
Write a short paragraph explaining what acceleration is and why a car is accelerating as it rounds a corner.
Acceleration is the rate which velocity changes. A car is accelerating when going around a corner because acceleration depends on velocity and velocity does not just depend on speed, but on direction. The change in direction leads to acceleration.
T/F? A ball is thrown into the air. At the highest point, the ball has zero velocity and zero acceleration.
False
T/F? As a ball falls freely, the distance it falls each second is the same.
False
T/F? Average speed is defined as the time it takes for a trip divided by the distance.
False
T/F? Unless stated otherwise, when we discuss the speeds of things, we mean with respect to the center of the universe.
False
Write a short paragraph on how fast things fall on Earth. Compare this to motion on the moon, where the acceleration due to gravity is about 1.6 m/s^2.
Gravity is what causes things to fall back to the earth. The acceleration due to gravity on the earth is 10 m/s^2. This is faster than the moon because the acceleration only increases 1.6 m/s^2 because it has a smaller gravitational force.
If you drop a feather and a coin at the same time in a vacuum tube, which will reach the bottom of the tube first?
Neither-they will both reach the bottom at the same time.
Explain the difference between speed and velocity, and give examples of both.
Speed is the rate that distance is covered while velocity is the speed in a given direction. An example of speed is a car driving at 45 miles per hour while an example of velocity is a car going 45 miles per hour North.
Acceleration
The rate at which velocity changes with time
T/F? Acceleration is the rate at which velocity changes
True
T/F? Even though a car is slowing down, it is still accelerating, in the most general definition of acceleration.
True
T/F? Velocity is different from speed in that velocity is speed in a given direction.
True
T/F? Velocity tells you how fast an object is moving, while distance tells you how far an object has moved.
True
T/F? When we discuss the motion of something, its motion is described relative to something else.
True
Suppose you are in a car that is going around a curve. The speedometer reads a constant 30 miles per hour. Which of the following is NOT true?
Your velocity is constant.
Suppose an object is in free fall. Each second the object falls
a larger distance than in the second before.
If a freely falling object were somehow equipped with a speedometer, its speed reading would increase each second by
about 10 m/s.
When something falls to the ground, it accelerates. This acceleration is called the acceleration due to gravity and is symbolized by the letter g. What is the value of g on Earth's surface?
about 10 m/s^2
A ball is thrown straight up. At the top of its path its acceleration is
about 10 m/s^2.
In the absence of air resistance, objects fall at constant
acceleration.
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.
Consider drops of water leaking from a water faucet. As the drops fall they
get farther apart.
When you look at the speedometer in a moving car, you can see the car's
instantaneous speed.
When a basketball player jumps to make a shot, once the feet are off the floor, the jumper's acceleration
is g; no more, no less.
The hang time (time one's feet are off the ground in a jump) for most athletes is
less than 1 second.
Unit of Acceleration
m/s^2
One possible unit of speed is
miles per hour, light years per century, kilometers per hour.
Acceleration is defined as
the rate at which velocity itself changes
A ball is thrown upwards and caught when it comes back down. In the absence of air resistance, the speed of the ball when caught would be
the same as the speed it had when thrown upwards.
Acceleration is defined as the CHANGE in
velocity divided by the time interval.
