### All AP Physics 1 Resources

## Example Questions

### Example Question #81 : Motion In One Dimension

A baseball batter hits a ball straight up in the air at a velocity of . If the ball hits the bat at a height of above the ground, how long does it take for the ball to hit the ground?

**Possible Answers:**

**Correct answer:**

There air multiple ways to solve this problem, so don't worry if you attacked this problem from a different angle. This following method avoids using the quadratic formula:

First, we will calculate how long it takes for the ball to travel upward, and then come back down to its original height.

Since we are neglecting air resistance, we know that our final velocity is equal but in the opposite direction as the initial velocity. Therefore, we get:

At this point, the ball is at it's original height of , but traveling downward at a rate of .

We can then use the following expression to calculate the velocity of the ball as it hits the ground:

Plugging in our values:

Then using our original expression again:

Adding our times together:

### Example Question #351 : Ap Physics 1

A plane is getting ready to take off and starts down the runway. The plane accelerates down the runway at a rate of and after seconds, it lifts off. How long did it travel on the runway before taking off?

**Possible Answers:**

**Correct answer:**

For this problem, the following kinematic equation is necessary:

Since the plane starts at rest, we can simplify the equation to

The problem defines the acceleration to be and the time to be seconds so

### Example Question #82 : Motion In One Dimension

A feather is dropped on the moon from a height of meters. How long does it take for the feather to fall to the surface?

**Possible Answers:**

**Correct answer:**

For this problem, the following kinematic equation is necessary:

Since the feather starts at rest, we can simplify the equation to

The problem defines the acceleration to be . Since the acceleration is in the downward direction (towards the surface), it is more appropriately written as . The distance is meters (also in the downward direction). Therefore,

### Example Question #83 : Motion In One Dimension

An ant travels along a taut string of length feet in minutes. What is the ant's average velocity in meters per second?

**Possible Answers:**

**Correct answer:**

First we convert our units to SI, feet is meters and minutes is seconds. Now we combine this dividing by to arrive at our average velocity of

### Example Question #81 : Motion In One Dimension

The tallest Pine tree in a nearby forest is 150 meters tall. If a pine cone situated at the very top of the tree fell, how long would it take to hit the ground?

**Possible Answers:**

4.0 seconds

12 seconds

5.5 seconds

6.2 seconds

15 seconds

**Correct answer:**

5.5 seconds

Since the pine cone starts from rest and we are given a distance we will use:

.

Solving for t:

*Note that the distance is negative since the object is falling and gravitational acceleration is downward. One could also just ignore the signs since time cannot be negative.

### Example Question #82 : Motion In One Dimension

The bottom of a mine shaft is filled with water to a depth of 5 feet. If a rock is dropped from the surface and is heard hitting the water 5 seconds later, how deep is the mine shaft? Use and consider the travel time of the sound waves negligible.

**Possible Answers:**

125 meters

150 meters

130 meters

100 meters

135 meters

**Correct answer:**

130 meters

Since the stone is dropped from rest and we are searching for a distance, we can use the kinematic equation :.

We can eliminate the second term, initial velocity times time because the stone is dropped.

But since the mine shaft is filled with 5 meters of water its actual depth would **130 meters.**

### Example Question #86 : Motion In One Dimension

A high powered cannon projectile leaves the barrel with a muzzle velocity of . If the barrel is 1.2 meters long, what is the acceleration of the bullet in the barrel? Assume uniform acceleration.

**Possible Answers:**

None of these

**Correct answer:**

The projectile started from rest and we are given its initial velocity, the muzzle velocity that is. Use the kinematic equation: .

The initial velocity is canceled out:

Solve for a:

### Example Question #87 : Motion In One Dimension

Some grasshoppers can jump up to 1.7 meters in the air. What is this insects take off speed from the ground?

**Possible Answers:**

None of these

**Correct answer:**

Use the kinematic equation . Note that the grasshoppers final speed will be equal to 0.

Square rooting both sides:

### Example Question #83 : Motion In One Dimension

If a person drops his keys on earth from 1.6 meters and an astronaut dropped hers on the moon, which set of keys would hit the ground first? Assume air friction is negligible on Earth and that both sets of sets of keys are the same mass.

**Possible Answers:**

The Earth because the pull of gravity is weaker.

The keys will hit the ground at the same time on both Earth and the Moon.

The Moon because the pull of gravity is weaker.

The Moon because the pull of gravity is stronger.

The Earth because the pull of gravity is stronger.

**Correct answer:**

The Earth because the pull of gravity is stronger.

The Earth's gravitational acceleration is approximately while the acceleration of gravity on the Moon is about 1.6. In other words the Earth's pull is much stronger than the Moon's. Objects will fall faster here on Earth.

### Example Question #84 : Motion In One Dimension

For a stone thrown straight up and caught at the same height it was thrown, which of the following are true. Ignore air friction.

**Possible Answers:**

Acceleration and velocity of the stone always point in the same direction.

Two of these

Acceleration of the stone is zero after being caught.

The time going up equals the time going down.

Acceleration of the stone is zero at the apex when the stone pauses for a split second.

**Correct answer:**

The time going up equals the time going down.

Gravity is the same at all heights with minor exceptions over great distances such as deep in the Earth and at 30,000 feet; gravity would be stronger that much closer to Earth.

Acceleration of gravity pulls everything downward- all the time and even if an object isn't moving. So acceleration and velocity can't always point in the same direction as the stones initial velocity points up.

The time traveling up will be equal to time falling as the motions just cancel each other. Gravity is slowing the stone as it travels upward until it stops very, very briefly and begins to accelerate and travel downward.

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