AP Physics 1 : AP Physics 1

Study concepts, example questions & explanations for AP Physics 1

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Example Questions

Example Question #153 : Linear Motion And Momentum

\displaystyle 2m tall man standing on a cliff that is \displaystyle 35m high throws a baseball completely horizontally off the cliff at a velocity of \displaystyle 36\frac{m}{s}, how far from the base of the cliff will the ball travel before hitting the ground?

Possible Answers:

\displaystyle 99m

\displaystyle 648m

\displaystyle 67m

\displaystyle 38m

\displaystyle 512m

Correct answer:

\displaystyle 99m

Explanation:

In order to find the distance that the ball travels horizontally one must multiply the velocity of the ball by the amount of time that the ball is traveling. Time in the air can be found by figuring out the amount of time that it takes for the ball to hit the ground relative to the vertical distance. Using the equation:

 \displaystyle d=V_{0}t+\frac{1}{2}at^{^{2}} 

where d is \displaystyle 37m (height of the cliff plus height of the man), \displaystyle V_{0} is equal to zero because there is no initial vertical velocity, and acceleration is equal to the gravity constant, time is found to be \displaystyle 2.75s. In order to find distance traveled horizontally, one can use the equation:

\displaystyle d=V_0t+\frac{1}{2}at^2

Because the vertical and horizontal axis are completely independent of each other there is no acceleration in the horizontal direction, the equation then becomes simplified to:

\displaystyle d=V_{0}t

After plugging in numbers

\displaystyle d=36*2.75

\displaystyle d=99m

Example Question #431 : Ap Physics 1

Two balls are thrown off the edge of a cliff of height \displaystyle h from the same location. Both balls are thrown with an initial velocity of \displaystyle \small v. The first ball is thrown horizontally and the second ball is thrown at and angle of \displaystyle \small 45^{\circ} above the horizontal. When the cliff is a particular height, let's call it \displaystyle h_{equal}, the two balls will land at the same spot on the ground.

Which of the following is true?

Possible Answers:

The ball thrown \displaystyle 45^{\circ} above the horizontal will only go further than the horizontally thrown ball if \displaystyle h< h_{equal}

The ball thrown \displaystyle 45^{\circ} above the horizontal will only go further than the horizontally thrown ball if \displaystyle h>h_{equal}

There are multiple cliff heights where the two balls will land at the same location

The ball thrown \displaystyle 45^{\circ} above the horizontal will always go further besides when \displaystyle h=h_{equal}

The horizontally thrown ball will always go further besides when \displaystyle h=h_{equal}

Correct answer:

The ball thrown \displaystyle 45^{\circ} above the horizontal will only go further than the horizontally thrown ball if \displaystyle h< h_{equal}

Explanation:

If \displaystyle h=0, the horizontally thrown ball will travel no distance. As the height of the cliff increases, the horizontally thrown ball will have more and more air time until it begins to travel further than the ball thrown \displaystyle 45^{\circ} above the horizontal. This is because the distance each ball will go equals the time it's in the air multiplied by its horizontal velocity (since it's not accelerating in the x-direction). The time the ball thrown \displaystyle 45^{\circ} above the horizontal is always the same amount greater than the time the ball thrown horizontally is in the air. The ball thrown horizontally has a horizontal velocity greater than the ball thrown \displaystyle 45^{\circ} above the horizontal (by a factor of \displaystyle \sqrt{2}). This means the ball thrown horizontally travels a distance of \displaystyle v*t while the ball thrown \displaystyle 45^{\circ} above the horizontal travels a distance of \displaystyle \frac{\sqrt2v(t+k)}{2}. If we equate these two expressions, we get \displaystyle t=(1+\sqrt{2})k. When \displaystyle t is less than this, the ball thrown \displaystyle 45^{\circ} above the horizontal travels further and when \displaystyle t is greater the ball thrown horizontally travels further. \displaystyle t=(1+\sqrt{2})k represents the time is takes for the ball thrown horizontally to hit the ground when the height of this cliff is \displaystyle h_{equal}.

Example Question #151 : Linear Motion And Momentum

Pulley

2 masses are connected to a pulley system as demonstrated by the image above. Mass 1 (m1) weighs \displaystyle 4.0\ kg and mass 2 weighs \displaystyle 6.5\ kg.

Assuming there is no friction in the system, how fast would mass 1 be accelerating?

Possible Answers:

\displaystyle 12\ \frac{m}{s^{2}}

\displaystyle 16\ \frac{m}{s^{2}}

\displaystyle 14\ \frac{m}{s^{2}}

\displaystyle 10\ \frac{m}{s^{2}}

\displaystyle 20\ \frac{m}{s^{2}}

Correct answer:

\displaystyle 16\ \frac{m}{s^{2}}

Explanation:

Because the mass of object 1 is given, the force acting on it must be found in order to figure out how fast it is accelerating. These 3 variables are related by the equation:

\displaystyle F=ma

Because there is no friction in the system, the only force acting on the object is the tension in the rope. The magnitude of the force of tension is the magnitude of the gravitational force of mass 2. Gravitational force is equal to:

\displaystyle F=mg

where g is the gravity constant which is equal to \displaystyle 9.81\frac{m}{s^{2}} which is also the acceleration of this object. Since this force is the only force acting on the object, accelerating can be found relating the 2 equations above as follows:

\displaystyle m_{2}g=m_{1}a_{1}

After plugging in values, the acceleration of mass 1 is found to be:

\displaystyle 6.5*9.81=4.0a_{1}

\displaystyle a_{1}\approx 16\ \frac{m}{s^{2}}

Example Question #434 : Ap Physics 1

If an object is launched \displaystyle 50\: \frac{m}{s} at an angle of \displaystyle 30^{o} with respect to the ground, what is its vertical speed after \displaystyle 2\: s?

Possible Answers:

\displaystyle 5.4\: \frac{m}{s}

\displaystyle 25\: \frac{m}{s}

\displaystyle 16.2\: \frac{m}{s}

\displaystyle 35.8\: \frac{m}{s}

\displaystyle 30.4\: \frac{m}{s}

Correct answer:

\displaystyle 5.4\: \frac{m}{s}

Explanation:

To solve this question, we'll first need to break up the velocity into its component parts. For this question, we're only concerned about motion in the vertical direction, so we'll first need to find the initial velocity in the vertical direction.

\displaystyle v_{yi}=v_{i}sin(\Theta )

\displaystyle v_{yi}=(50\: \frac{m}{s})sin(30^{o})=25\: \frac{m}{s}

Now that we know what the initial velocity is, we can determine what the final velocity will be after \displaystyle 2\: s.

\displaystyle \frac{\Delta v}{t}=a

\displaystyle \frac{v_{yf}-v_{yi}}{t}=a

\displaystyle v_{yf}=v_{yi}+at

\displaystyle v_{yf}=25\: \frac{m}{s}+(-9.8\: \frac{m}{s^{2}})(2\:sec)

\displaystyle v_{yf}=25\: \frac{m}{s}-19.6\: \frac{m}{s}=5.4\: \frac{m}{s}

Example Question #155 : Linear Motion And Momentum

A baseball hits a perfectly horizontal ball at a speed of \displaystyle 17\frac{m}{s} from a height of \displaystyle 1.2m. How far has the ball traveled before it hits the ground?

\displaystyle g = 10\frac{m}{s^2}

Possible Answers:

\displaystyle 8.3m

\displaystyle 7.6m

\displaystyle 6.1m

\displaystyle 4.2m

\displaystyle 1.9m

Correct answer:

\displaystyle 8.3m

Explanation:

First, we can calculate how long it takes for the ball to hit the ground using the following expression:

\displaystyle \Delta y = v_{i}+\frac{1}{2}at^2

Since the original vertical velocity is 0, we can rearrange to get:

\displaystyle t = \sqrt{\frac{2\Delta y}{a}}

Plugging in our values, we get:

\displaystyle t = \sqrt{\frac{2(1.2m)}{10\frac{m}{s^2}}}

\displaystyle t = 0.49s

Multiplying this by the velocity given in the problem statement (horizontal velocity), we get:

\displaystyle d = \left ( 17\frac{m}{s}\right )(0.49s) = 8.3m

Example Question #436 : Ap Physics 1

A baseball player hits a ball from a height of \displaystyle 1m at a velocity of \displaystyle 30\frac{m}{s} and an angle of \displaystyle 15^{\circ} above the horizontal. The ball is hit toward another player that is \displaystyle 25m away from the batter. At what height is the ball when it reaches the other player?

\displaystyle g = 10\frac{m}{s^2}

Possible Answers:

\displaystyle 2.41m

\displaystyle 1.77m

\displaystyle 0.16m

\displaystyle 3.98m

\displaystyle 0.99m

Correct answer:

\displaystyle 3.98m

Explanation:

First, let's separate the given velocity into its vertical and horizontal components:

\displaystyle v_x = vcos(\theta)

\displaystyle v_y = vsin(\theta)

\displaystyle v_x= \left ( 30\frac{m}{s}\right )cos(15^{\circ})

\displaystyle v_y= \left ( 30\frac{m}{s}\right )sin(15^{\circ})

\displaystyle v_ x= 28.97777\frac{m}{s}

\displaystyle v_y = 7.76457\frac{m}{s}

Since we are neglecting air resistance, we can easily calculate how long it takes for the ball to reach the second player:

\displaystyle t = \frac{d}{v_x}=\frac{25m}{28.97777\frac{m}{s}} = 0.86273s

Now we can use this time to calculate the height of the ball when it reaches the second player:

\displaystyle y_f = y_i+v_{y_i}t+\frac{1}{2}at^2

Plugging in our values, we get:

\displaystyle y_f = 1m+\left ( 7.76457\frac{m}{s}\right )(0.86273s)+\frac{1}{2}\left ( -10\frac{m}{s^2}\right )(0.86273s)^2

\displaystyle y_f=3.98m

Example Question #61 : Motion In Two Dimensions

A batter hits a ball at an angle of \displaystyle 50^{\circ} to the horizontal. If the home run fence is \displaystyle 120m away with a height the same as when the batter hits the ball, what is the minimal initial velocity that will result in a home run? 

 \displaystyle g = 10\frac{m}{s^2}

Possible Answers:

\displaystyle 41.3\frac{m}{s}

\displaystyle 34.9\frac{m}{s}

\displaystyle 38.2\frac{m}{s}

\displaystyle 44.4\frac{m}{s}

\displaystyle 31.7\frac{m}{s}

Correct answer:

\displaystyle 34.9\frac{m}{s}

Explanation:

This problem is greatly simplified since the home run fence has the same height as the initial height of the ball. Therefore, we can use this range equation to solve this problem in one calculation: 

\displaystyle R = \frac{v_o^2sin(2\theta)}{g}

Rearranging for velocity, we get:

\displaystyle v_o = \sqrt{\frac{R\cdot g}{sin(2\theta)}}

Plugging in our values, we get:

\displaystyle v_o = \sqrt{\frac{(120m)\left ( 10\frac{m}{s^2}\right )}{sin(100^{\circ})}}

\displaystyle v_o = 34.9\frac{m}{s}

Example Question #62 : Motion In Two Dimensions

A batter hits a ball at an angle of \displaystyle 50^{\circ} to the horizontal. If the home run fence is \displaystyle 120m away with a height of \displaystyle 5m, and the ball is hit from an initial height of \displaystyle 1m, what is the minimal initial velocity that will result in a home run? 

\displaystyle g = 10\frac{m}{s^2}

Possible Answers:

\displaystyle 35.4\frac{m}{s}

\displaystyle 25.0\frac{m}{s}

\displaystyle 27.9\frac{m}{s}

\displaystyle 34.6\frac{m}{s}

\displaystyle 31.8\frac{m}{s}

Correct answer:

\displaystyle 35.4\frac{m}{s}

Explanation:

There are multiple ways to attack this problem, so don't worry if you took a different route. However, no matter which way you go, you'll be substituting small expressions into larger ones.

First, let's develop an expression of how long it takes the ball to reach the home run fence. We know that:

 \displaystyle d = v_x\cdot t

Rearranging for time:

\displaystyle t = \frac{d}{v_x}

Then we can substitute the following expression in for horizontal velocity:

\displaystyle v_x = vcos(\theta)

\displaystyle t = \frac{d}{vcos(\theta)}

Now that we have an expression for time, we can use the following expression:

\displaystyle \Delta y= v_{y_i}t+\frac{1}{2}at^2

Plugging in an expression for initial vertical velocity, we get:

\displaystyle \Delta y= vsin(\theta)t+\frac{1}{2}at^2

Plugging in our expression for time, we get:

\displaystyle \Delta y=vsin(\theta)\left (\frac{d}{vcos(\theta)} \right )+\frac{1}{2}a\left ( \frac{d}{vcos(\theta)}\right )^2

Now let's simplify this a bit:

\displaystyle \Delta y =d\cdot tan(\theta)+\frac{a\cdot d^2}{2v^2cos^2(\theta)}

Rearranging:

\displaystyle \Delta y -d\cdot tan(\theta)=\frac{a\cdot d^2}{2v^2cos^2(\theta)}

And some more:

\displaystyle 2v^2cos^2(\theta)=\frac{a\cdot d^2}{\Delta y -d\cdot tan(\theta)}

One last time:

\displaystyle v = \sqrt{\frac{a\cdot d^2}{\left ( \Delta y - d\cdot tan\theta\right )\left ( 2cos^2\theta\right )}}

It may look a bit nasty, but we know all of these values, so time to plug and chug:

\displaystyle v = \sqrt{\frac{\left ( 10\frac{m}{s^2}\right )(120m)^2}{\left ( 4m-(120m)tan(50^\circ)\right )(2cos^2(50^{\circ}))}}

\displaystyle v_i = 35.4\frac{m}{s}

Example Question #71 : Motion In Two Dimensions

A home run derby is being held in a stadium where the home run wall is \displaystyle 100m from home plate. The wall itself has a height of \displaystyle 5m. The stands begin at the wall and with equal height, and rise at an angle of \displaystyle 30^{\circ} to the horizontal.

\displaystyle g = 10\frac{m}{s^2}

If a home run is hit a total distance of \displaystyle 120 m from an initial height of \displaystyle 1m and an angle of \displaystyle 50^{\circ} to the horizontal, what is the ball's initial velocity?

Possible Answers:

\displaystyle 45.9\frac{m}{s}

\displaystyle 14.3\frac{m}{s}

\displaystyle 29.9\frac{m}{s}

\displaystyle 21.2\frac{m}{s}

\displaystyle 36.8\frac{m}{s}

Correct answer:

\displaystyle 36.8\frac{m}{s}

Explanation:

From the problem statement, we can use the following piecewise function to express the effective "height" at any point within the stadium:

If   \displaystyle x < 100m   then   \displaystyle y = 0m

If   \displaystyle x\geq 100m   then   \displaystyle y = 5m+(x-100)sin(30^{\circ})

Before, moving on, make sure you understand the reasoning of this function. The wall begins at a distance of \displaystyle 100m, a height of \displaystyle 5m, and rises at an angle of \displaystyle 30^{\circ}.

Using the total horizontal distance traveled, we can calculate the ball's final height using the above expression:

\displaystyle y = 5m+(120m-100m)sin(30^{\circ}) = 15m

Now we can use the following two kinematics expression:

\displaystyle \Delta y = v_{y_{i}}t+\frac{1}{2}at^2

\displaystyle t = \frac{d}{v_{x_{i}}}

Where d is the horizontal distance traveled. Replacing out component velocities, we get:

\displaystyle \Delta y = v_isin(\theta)t+\frac{1}{2}at^2

\displaystyle t = \frac{d}{v_icos(\theta)}

Substituting our expression for time into the other expression, we get:

\displaystyle \Delta y = dtan(\theta)+\frac{1}{2}a\left ( \frac{d}{v_icos(\theta)}\right )^2

Simplifying, we get:

\displaystyle \Delta y = dtan(\theta)+\frac{ad^2}{2v_i^2cos^2(\theta)}

Rearranging:

\displaystyle \frac{ad^2}{2v_i^2cos^2(\theta)} = dtan(\theta)-\Delta y

And again:

\displaystyle \frac{ad^2}{dtan(\theta)-\Delta y} = 2v_i^2cos^2(\theta)

One last time:

\displaystyle v_i = \sqrt{\frac{ad^2}{2cos^2(\theta)\left (dtan(\theta)-\Delta y \right )}}

It's nice and messy, but we have all of these values, so time to plug and chug:

\displaystyle v_i = \sqrt{\frac{\left ( 10\frac{m}{s^2}\right )(120m)^2}{2cos^2(50^{\circ})((120m)tan(50^{\circ})-14m)}}

\displaystyle v_i = 36.8\frac{m}{s}

Example Question #72 : Motion In Two Dimensions

A home run derby is being held in a stadium where the home run wall is \displaystyle 100m from home plate. The wall itself has a height of \displaystyle 5m. The stands begin at the wall and with equal height, and rise at an angle of \displaystyle 30^{\circ} to the horizontal.

\displaystyle g = 10\frac{m}{s^2}

A ball is hit with an initial vertical velocity of \displaystyle 25\frac{m}{s}  from a height of \displaystyle 1m. If it takes \displaystyle 4s for the ball to land in the stands, what is the total horizontal distance traveled?

Possible Answers:

\displaystyle 92m

\displaystyle 161m

\displaystyle 101m

\displaystyle 132m

\displaystyle 116m

Correct answer:

\displaystyle 132m

Explanation:

From the problem statement, we can use the following piecewise function to express the effective "height" at any point within the stadium:

If   \displaystyle x < 100m   then   \displaystyle y = 0m

If   \displaystyle x\geq 100m   then   \displaystyle y = 5m+(x-100)sin(30^{\circ})

Before, moving on, make sure you understand the reasoning of this function. The wall begins at a distance of \displaystyle 100m, a height of \displaystyle 5m, and rises at an angle of \displaystyle 30^{\circ}.

We can use the following expression to calculate the final height of the ball:

\displaystyle y_f= y_i + v_{y_{i}}t+\frac{1}{2}at^2

Plugging in our values, we get:

\displaystyle y_f = 1m + \left ( 25\frac{m}{s}\right )(4s)+\frac{1}{2}\left ( -10\frac{m}{s^2}\right )(4s)^2

\displaystyle y_f = 21m

Then we can use the piecewise expression to determine to total horizontal distance traveled:

\displaystyle 21m = 5m+ (x-100m)sin(30^{\circ})

\displaystyle x = \frac{16m}{sin(30^{\circ})}+100m

\displaystyle x = 132m

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