AP Physics 1 : Linear Motion and Momentum

Study concepts, example questions & explanations for AP Physics 1

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Example Questions

Example Question #51 : Motion In Two Dimensions

A quarterback throws a football a horizontal distance of \(\displaystyle 50 yd\) to a wide receiver. The ball was airborne for \(\displaystyle 5 s\). The ball had an initial speed of \(\displaystyle 50 mph\). The ball has a mass of \(\displaystyle .43kg\).

\(\displaystyle 1mph=.447\frac{m}{s}\)

\(\displaystyle 1 yd=.914 m\)

Determine the speed at the apex of the throw.

Possible Answers:

\(\displaystyle 9.81\frac{m}{s}\)

\(\displaystyle 9.44\frac{m}{s}\)

\(\displaystyle 9.14\frac{m}{s}\)

None of these

\(\displaystyle 10.2\frac{m}{s}\)

Correct answer:

\(\displaystyle 9.14\frac{m}{s}\)

Explanation:

At the apex, the only velocity will be in the \(\displaystyle x\) direction as the ball is at it's maximum height.

Using:

\(\displaystyle d_x=v_x*t\)

Solving for velocity

\(\displaystyle v_x=\frac{d_x}{t}\)

Converting yards to meters

\(\displaystyle 50yards*\frac{.914 meters}{1 yard}=45.7 meters\)

Plugging in values

\(\displaystyle v_x=\frac{45.7}{5}\)

\(\displaystyle v_x=9.14\frac{m}{s}\)

Example Question #60 : Motion In Two Dimensions

A quarterback throws a football a horizontal distance of \(\displaystyle 50 yd\) to a wide receiver. The ball was airborne for \(\displaystyle 5 s\). The ball had an initial speed of \(\displaystyle 50 mph\). The ball has a mass of \(\displaystyle .43kg\).

\(\displaystyle 1mph=.447\frac{m}{s}\)

\(\displaystyle 1 yd=.914 m\)

Determine the speed of the football 4 seconds after the throw.

Possible Answers:

None of these

\(\displaystyle < 9.14,-19.2>\frac{m}{s}\)

\(\displaystyle < 9.14,19.2>\frac{m}{s}\)

\(\displaystyle < 9.14,-10.1>\frac{m}{s}\)

\(\displaystyle < -9.14,-19.2>\frac{m}{s}\)

Correct answer:

\(\displaystyle < 9.14,-19.2>\frac{m}{s}\)

Explanation:

Determining horizontal component of velocity:

\(\displaystyle d_x=v_x*t\)

\(\displaystyle v_x=\frac{d_x}{t}\)

\(\displaystyle v_x=\frac{45.7}{5}\)

\(\displaystyle v_x=9.14\frac{m}{s}\)

Using

\(\displaystyle v_x^2+v_y^2=v^2\)

Solving for \(\displaystyle v_y\)

\(\displaystyle v_y=\sqrt{v^2-v_x^2}\)

Combining equations

\(\displaystyle v_y=\sqrt{v^2-(\frac{d_x}{t})^2}\)

Converting \(\displaystyle mph\) to \(\displaystyle mps\)

 \(\displaystyle 50mph*\frac{.447mps}{1 mph}=22.35\frac{m}{s}\)

Converting yards to meters

\(\displaystyle 50yards*\frac{.914 meters}{1 yard}=45.7 meters\)

Plugging in values:

\(\displaystyle v_y=\sqrt{v^2-(\frac{d_x}{t})^2}\)

\(\displaystyle v_y=\sqrt{22.35^2-(\frac{45.7}{5})^2}\)

\(\displaystyle v_y=20.4\frac{m}{s}\)

\(\displaystyle \overrightarrow{v}=< 9.14,20.4>\frac{m}{s}\)

Using

\(\displaystyle v_i+a*t=v_f\)

\(\displaystyle < 9.14,20.4>+< 0,-9.8>*4=v_f\)

\(\displaystyle < 9.14,-19.2>\frac{m}{s}=v_f\)

Example Question #61 : Motion In Two Dimensions

Two space ships are racing deep in space. At \(\displaystyle t=0\), Spaceship A is at the origin while traveling at \(\displaystyle < 600,400> \frac{m}{s}\). It is coasting, with it’s rockets off. Spaceship B is at \(\displaystyle < -600,-400>m\). It’s traveling at \(\displaystyle < 150,100>\frac{m}{s}\). It’s rockets are firing with a constant force of \(\displaystyle < 1.5*10^6N, 1*10^6N>\). Both rockets have a mass of \(\displaystyle 1.5*10^5 kg\).

At what time will spaceship B pass Spaceship A if this continues? Assume that they are at different locations in the z-axis and thus will not crash.

Possible Answers:

\(\displaystyle t=98.9s\)

None of these

\(\displaystyle t=91.3s\)

\(\displaystyle t=46.7s\)

\(\displaystyle t=12.5s\)

Correct answer:

\(\displaystyle t=91.3s\)

Explanation:

Using position update formula:

\(\displaystyle r=r_i+v_i*t+.5at^2\)

The positions need to be equal, so:

\(\displaystyle r_i_B+v_i_B*t+.5a_Bt^2=r_i_A+v_i_A*t+.5a_At^2\)

Converting into quadratic form:

\(\displaystyle 0=(.5a_B-.5a_A)t^2+(v_i_B-v_i_A)t+(r_i_B-r_i_A)\)

Plugging in values:

\(\displaystyle 0=(.5< 10,6.66>-.5*< 0,0>)t^2+(< 150,100>-< 600,400>)t+(< -600,-400>-< 0,0>)\)

\(\displaystyle 0=< 5t^2,3.33t^2>+< -450t,-300t>+< -600,-400>\)

\(\displaystyle 0=5t^2-450t-600\)

\(\displaystyle 0=3.33t^2-300t-400\)

Solving for a quadratic yields:

\(\displaystyle t=91.3s\)

Example Question #62 : Motion In Two Dimensions

Two space ships are racing deep in space. At \(\displaystyle t=0\), Spaceship A is at the origin while traveling at \(\displaystyle < 600,400> \frac{m}{s}\). It is coasting, with it’s rockets off. Spaceship B is at \(\displaystyle < -600,-400>m\). It’s traveling at \(\displaystyle < 150,100>\frac{m}{s}\). It’s rockets are firing with a constant force of \(\displaystyle < 1.5*10^6N, 1*10^6N>\). Both rockets have a mass of \(\displaystyle 1.5*10^5 kg\).

What magnitude velocity will spaceship \(\displaystyle B\) have at the origin?

Possible Answers:

\(\displaystyle 388\frac{m}{s}\)

\(\displaystyle 175\frac{m}{s}\)

\(\displaystyle 229\frac{m}{s}\)

None of these

\(\displaystyle 325\frac{m}{s}\)

Correct answer:

\(\displaystyle 229\frac{m}{s}\)

Explanation:

Using

\(\displaystyle W=E_f-E_i\)

\(\displaystyle F*d=.5mv_f^2-.5mv_i^2\)

Solving for \(\displaystyle v_f\)

\(\displaystyle \sqrt{\frac{F*d+.5mv_i^2}{.5m}}=v_f\)

Plugging in values:

\(\displaystyle \sqrt{\frac{< 1.5*10^6,1.5*10^6>*< 600,400>+.5*1.5*10^5*180.3^2}{.5(1.5*10^5)}}=v_f\)

\(\displaystyle v_f=229\frac{m}{s}\)

Example Question #63 : Motion In Two Dimensions

\(\displaystyle 2m\) 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:

\(\displaystyle 648m\)

\(\displaystyle 67m\)

\(\displaystyle 512m\)

\(\displaystyle 38m\)

\(\displaystyle 99m\)

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 #64 : Motion In Two Dimensions

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

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

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 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 \(\displaystyle h< h_{equal}\)

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 #65 : Motion In Two Dimensions

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:

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

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

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

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

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

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 #66 : Motion In Two Dimensions

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:

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

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

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

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

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

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 #67 : Motion In Two Dimensions

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:

\(\displaystyle 6.1m\)

\(\displaystyle 1.9m\)

\(\displaystyle 4.2m\)

\(\displaystyle 7.6m\)

\(\displaystyle 8.3m\)

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 #68 : Motion In Two Dimensions

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:

\(\displaystyle 1.77m\)

\(\displaystyle 0.16m\)

\(\displaystyle 0.99m\)

\(\displaystyle 2.41m\)

\(\displaystyle 3.98m\)

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:

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

\(\displaystyle y_f=3.98m\)

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