AP Physics 1 : AP Physics 1

Study concepts, example questions & explanations for AP Physics 1

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Example Questions

Example Question #201 : Linear Motion And Momentum

A train of mass \displaystyle 1.8\times10^7 kg traveling at \displaystyle 15 \frac{m}{s}strikes a car stuck on the tracks of mass \displaystyle 1300 kg.

 

Determine the initial momentum of the system.

Possible Answers:

None

\displaystyle 5.7\times10^8 kg\frac{m}{s}

\displaystyle 2.4\times10^7 kg\frac{m}{s}

\displaystyle 1.7\times10^8 kg\frac{m}{s}

\displaystyle 2.7\times10^8 kg\frac{m}{s}

Correct answer:

\displaystyle 2.7\times10^8 kg\frac{m}{s}

Explanation:

\displaystyle P_{total}=P_1+P_2.......

 

The train and car are our only two objects in the system.

 

The initial momentum of the car is zero.

 

So the only momentum that will contribute is that of the train.

 

\displaystyle p=mv

 

\displaystyle p=1.8\times10^7\cdot15

 

Plugging in our values, we get \displaystyle 2.7\times10^8 kg\frac{m}{s}

Example Question #21 : Impulse And Momentum

A train of mass \displaystyle 1.8\times10^7 kg traveling at \displaystyle 15 \frac{m}{s}strikes a car stuck on the tracks of mass \displaystyle 1300 kg. The car becomes stuck on the train.

 

Determine the final velocity of the train.

Possible Answers:

\displaystyle 15 \frac{m}{s}

\displaystyle 20 \frac{m}{s}

\displaystyle 30 \frac{m}{s}

\displaystyle 10 \frac{m}{s}

None of these

Correct answer:

\displaystyle 15 \frac{m}{s}

Explanation:

We will need to use conservation of momentum to solve this problem.

 

\displaystyle M_1V_1+M_2V_2=M_{final}V_{final}

 

Where \displaystyle M_1 and \displaystyle V_1 refer to the train, and \displaystyle M_2 and \displaystyle V_2 refer to the car. \displaystyle M_{final}and \displaystyle V_{final} refer to the final state of both the train and the car.

 

Rearranging using algebra......

 

\displaystyle \frac{M_1V_1+M_2V_2}{M_{final}}=V_{final}

 

\displaystyle \frac{1.8\times10^7\cdot15+1300\cdot0}{1.8\times10^7}=V_{final}

 

Plugging in our values, we get \displaystyle 15 \frac{m}{s}.

Example Question #22 : Impulse And Momentum

A train of mass \displaystyle 1.8\times10^7 kg traveling at \displaystyle 15 \frac{m}{s}strikes a car stuck on the tracks of mass \displaystyle 1300 kg. The car becomes stuck on the train.

 

Determine the final velocity of the car.

Possible Answers:

None of these

\displaystyle 15 \frac{m}{s}

\displaystyle 5 \frac{m}{s}

\displaystyle 20 \frac{m}{s}

\displaystyle 10 \frac{m}{s}

Correct answer:

\displaystyle 15 \frac{m}{s}

Explanation:

We will need to use conservation of momentum to solve this problem.

 

\displaystyle M_1V_1+M_2V_2=M_{final}V_{final}

 

Where \displaystyle M_1 and \displaystyle V_1 refer to the train, and \displaystyle M_2 and \displaystyle V_2 refer to the car. \displaystyle M_{final}and \displaystyle V_{final} refer to the final state of both the train and the car.

 

Rearranging using algebra......

 

\displaystyle \frac{M_1V_1+M_2V_2}{M_{final}}=V_{final}

 

\displaystyle \frac{1.8\times10^7\cdot15+1300\cdot0}{1.8\times10^7}=V_{final}

 

Plugging in our values, we get \displaystyle 15 \frac{m}{s}.

Example Question #23 : Impulse And Momentum

A train of mass \displaystyle 1.8\times10^7 kg traveling at \displaystyle 15 \frac{m}{s} strikes a car stuck on the tracks of mass \displaystyle 1300 kg.

 

Let's assume this collison took \displaystyle .01 seconds to happen. That is, it took the car \displaystyle .01 seconds to accelerate to it's new velocity. Determine the force experienced by the car.

Possible Answers:

\displaystyle 1.95\times10^6 N

\displaystyle 2.25\times10^6 N

\displaystyle 3.38\times10^6 N

None of these

\displaystyle 1.11\times10^6 N

Correct answer:

\displaystyle 1.95\times10^6 N

Explanation:

We will need to use conservation of momentum to solve this problem.

 

\displaystyle M_1V_1+M_2V_2=M_{final}V_{final}

 

Where \displaystyle M_1 and \displaystyle V_1 refer to the train, and \displaystyle M_2 and \displaystyle V_2 refer to the car. \displaystyle M_{final}and \displaystyle V_{final} refer to the final state of both the train and the car.

 

Rearranging using algebra......

 

\displaystyle \frac{M_1V_1+M_2V_2}{M_{final}}=V_{final}

 

\displaystyle \frac{1.8\times10^7\cdot15+1300\cdot0}{1.8\times10^7}=V_{final}

 

Plugging in our values, we get \displaystyle 15 \frac{m}{s}.

 

 

 

Then, we will need to find out final momentum of the car.

 

 

\displaystyle M_{car}V_{final}=P_{final}

\displaystyle 1300kg\cdot15\frac{m}{s}=P_{final}

\displaystyle M_{car}V_{final}=P_{final}

 

 \displaystyle \Delta P=P_{final}-P_{initial}

 

Since our intial momentum of the car was \displaystyle 0, our change in momentum will be equal to the \displaystyle P_{final}.

 

 

 \displaystyle \Delta P=P_{final}

 

We will use the definition of impulse, which is the change in momentum:

 

\displaystyle F\cdot \Delta t= \Delta P

 

We will use substitution:

 

\displaystyle F\cdot \Delta t= P_{final}

 

Plugging in our values, we get \displaystyle 1.95\times10^6 N

Example Question #24 : Impulse And Momentum

A car of mass \displaystyle 1110kg is accelerated from \displaystyle 10 \frac{m}{s} to \displaystyle 35 \frac{m}{s} in 2s.

Determine the average total forces on this car during this time frame.

Possible Answers:

\displaystyle F=1.4*10^4N

\displaystyle F=2.4*10^4N

\displaystyle F=4.4*10^4N

\displaystyle F=1.1*10^4N

\displaystyle F=3.9*10^4N

Correct answer:

\displaystyle F=1.4*10^4N

Explanation:

Determine the change in the velocity of the car:

\displaystyle 35\frac{m}{s}-10\frac{m}{s}=25\frac{m}{s}

Calculate the average acceleration:

\displaystyle \frac{25\frac{m}{s}}{2 s}=\frac{\Delta v}{\Delta s}=a

\displaystyle 12.5\frac{m}{s^2}=a

Use the definition of force:

\displaystyle F=ma

\displaystyle F=1110kg*12.5\frac{m}{s^2}

\displaystyle F=1.4*10^4N

Example Question #25 : Impulse And Momentum

A cart is traveling at \displaystyle 3 \frac{m}{s} when it launches a ball straight into the air with initial velocity \displaystyle 15 \frac{m}{s}.

You may ignore air resistance.

How much time will the ball take from the moment it is launched to return to it's initial height?

Possible Answers:

None of these

\displaystyle \Delta t_{airtime}=4.5s

\displaystyle \Delta t_{airtime}=30s

\displaystyle \Delta t_{airtime}=1.5s

\displaystyle \Delta t_{airtime}=3.0s

Correct answer:

\displaystyle \Delta t_{airtime}=3.0s

Explanation:

First, break the airborne time into two pieces, the ascent and descent.

Ascent:

The ball will need to decelerate from \displaystyle 15\frac{m}{s} to \displaystyle 0 \frac{m}{s}.

Use acceleration due to gravity.

\displaystyle 15\frac{m}{s}-9.8\frac{m}{s^2}*\Delta t=0\frac{m}{s}

Solve for \displaystyle \Delta t

\displaystyle \Delta t=1.5s

Descent:

Due to parabolic motion, the ball will have the same magnitude of velocity when it returns to it's height as when it launched, albeit in the opposite direction.

\displaystyle 0\frac{m}{s}-9.8\frac{m}{s^2}*\Delta t=-15\frac{m}{s}

Solving for \displaystyle \Delta t

\displaystyle \Delta t=1.5s

Add the times together to get the total airtime.

\displaystyle \Delta t_{airtime}=3.0s

Example Question #26 : Impulse And Momentum

A cart is traveling at \displaystyle 3 \frac{m}{s} when it launches a ball straight into the air with initial velocity \displaystyle 15 \frac{m}{s}. Ignore air resistance.

How far will the cart have traveled by the time the ball returns to it's initial height?

Possible Answers:

None of these

\displaystyle 9m=d

\displaystyle 3.5m=d

\displaystyle 25m=d

\displaystyle 15m=d

Correct answer:

\displaystyle 9m=d

Explanation:

First, break the airborne time into two pieces, the ascent and descent.

Ascent:

The ball will need to decelerate from \displaystyle 15\frac{m}{s} to \displaystyle 0 \frac{m}{s}.

Use acceleration due to gravity.

\displaystyle 15\frac{m}{s}-9.8\frac{m}{s^2}*\Delta t=0\frac{m}{s}

Solve for \displaystyle \Delta t

\displaystyle \Delta t=1.5s

Descent:

Due to parabolic motion, the ball will have the same magnitude of velocity when it returns to it's height as when it launched, albeit in the opposite direction.

\displaystyle 0\frac{m}{s}-9.8\frac{m}{s^2}*\Delta t=-15\frac{m}{s}

Solve for \displaystyle \Delta t

\displaystyle \Delta t=1.5s

Add the times together.

\displaystyle \Delta t_{airtime}=3.0s

Multiply the airtime by the velocity of the cart.

\displaystyle 3.0s*\frac{3m}{s}=d

\displaystyle 9m=d

Example Question #21 : Impulse And Momentum

An astronaut of mass \displaystyle 100kg throws a \displaystyle 8kg shot put in space. If the shot put has a magnitude of velocity of \displaystyle 3\frac{m}{s} in relation to the center of the galaxy, determine the magnitude of velocity of the astronaut in relation to the center of the galaxy.

Possible Answers:

\displaystyle v_a=15\frac{m}{s}

\displaystyle v_a=4\frac{m}{s}

\displaystyle v_a=32\frac{m}{s}

None of these

\displaystyle v_a=.32\frac{m}{s}

Correct answer:

\displaystyle v_a=.32\frac{m}{s}

Explanation:

Using conservation of momentum:

\displaystyle P_i=P_f

The initial momentum can be taken as zero from our reference frame.

\displaystyle 0\frac{kg*m}{s}=P_{astro}+P_{shotput}

Plug in values:

\displaystyle 0\frac{kg*m}{s}=100kg*v_a+8kg*-4\frac{m}{s}

Note: The sign of the velocity for the shot put is negative because it will be in the opposite direction as the astronaut. The question is asking for magnitude though, so we know it will be positive regardless of the direction since magnitude does not take into account the direction of motion.

\displaystyle v_a=.32\frac{m}{s}

Example Question #481 : Ap Physics 1

A batter makes contact with a baseball for 0.1 seconds, exerting a constant force of 100 Newtons during the contact.

What is the ball's change in momentum as a result of the contact?

Possible Answers:

\displaystyle 5Ns

\displaystyle 1Ns

\displaystyle 100Ns

\displaystyle 50Ns

\displaystyle 10 Ns

Correct answer:

\displaystyle 10 Ns

Explanation:

We use the equation: 

\displaystyle \Delta p = F \Delta t 

Where the change in momentum is \displaystyle \Delta p.

The force, \displaystyle F, is \displaystyle 100N and t is the time during which the force is exerted (\displaystyle \Delta t=0.1s) as given by the problem statement, we plug in to the formula:

\displaystyle \Delta p=(100N)*(0.1s)=10Ns

Example Question #29 : Impulse And Momentum

A locomotive of mass \displaystyle 167*10^3kg traveling at \displaystyle 4\frac{km}{hr}couples to a motionless \displaystyle 67*10^3kg coach without applying the brakes. Calculate the momentum change (the impulse experienced) of the coach.

Possible Answers:

\displaystyle 85.1*10^3\frac{kg*m}{s}

\displaystyle 47.8*10^3\frac{kg*m}{s}

\displaystyle 91.1*10^3\frac{kg*m}{s}

\displaystyle 66.7*10^3\frac{kg*m}{s}

\displaystyle 52.3*10^3\frac{kg*m}{s}

Correct answer:

\displaystyle 52.3*10^3\frac{kg*m}{s}

Explanation:

Use conservation of momentum

\displaystyle P_i=P_f

\displaystyle m_{1i}v_{1i}+m_{2i}v_{2i}=m_{1,2f}v_{1,2f}

Plug in values:

\displaystyle (167*10^3)*4+(67*10^3)*0=(234*10^3)v_{1,2f}

Solve for \displaystyle v_{1,2f}:

\displaystyle v_{1,2f}=\frac{167*10^3*4}{234*10^3}

\displaystyle v_{1,2f}=2.85\frac{km}{hr}

Definition of impulse:

\displaystyle J=\Delta P=m(v_f-v_i)

Convert \displaystyle \frac{km}{hr} to \displaystyle \frac{m}{s}

\displaystyle 2.85\frac{km}{hr}*\frac{1hr}{3600s}*\frac{1000m}{1km}=.79\frac{m}{s}

Plug in values:

\displaystyle J=\Delta P=67*10^3(.79-0)

\displaystyle J=52.3*10^3\frac{kg*m}{s}

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