AP Physics 1 : Linear Motion and Momentum

Study concepts, example questions & explanations for AP Physics 1

varsity tutors app store varsity tutors android store

Example Questions

Example Question #61 : Motion In One Dimension

A car traveling at \(\displaystyle 20 \frac{m}{s}\) sees a red light ahead and begins to slow down. The gas pedal is not touched until after the car has left the intersection. It takes \(\displaystyle 5s\) to reach the light, which turns green again before the car comes to a complete stop. At this point the car rolls through the intersection at \(\displaystyle 5 \frac{m}{s}\). What was the car's acceleration during this time?  

Possible Answers:

\(\displaystyle .33 \frac{m}{s^{2}}\)

\(\displaystyle -.33 \frac{m}{s^{2}}\)

\(\displaystyle 3 \frac{m}{s^{2}}\)

\(\displaystyle -3 \frac{m}{s^{2}}\)

Correct answer:

\(\displaystyle -3 \frac{m}{s^{2}}\)

Explanation:

The equation for acceleration is \(\displaystyle \frac{\Delta v}{\Delta t}\). The final velocity minus the initial velocity is \(\displaystyle -15 \frac{m}{s}\) and the change in time is \(\displaystyle 5s\). When dividing the change in velocity by the change in time you receive the answer \(\displaystyle -3 \frac{m}{s^{2}}\) which means that the car is decelerating due to the negative sign.

Example Question #61 : Linear Motion And Momentum

While riding a bike down a steep hill at \(\displaystyle 9\frac{m}{s}\) you skid to a stop in 3.2 seconds. How far did the bike slide? Assume uniform acceleration.

Possible Answers:

\(\displaystyle \Delta x=4.4m\)

\(\displaystyle \Delta x=12.0m\)

\(\displaystyle \Delta x=14.4m\)

\(\displaystyle \Delta x=1.4m\)

\(\displaystyle \Delta x=10.4m\)

Correct answer:

\(\displaystyle \Delta x=14.4m\)

Explanation:

\(\displaystyle \Delta x= (\frac{V_{i}+V_{f}}{2})*t=\frac{9\frac{m}{s}}{2}*3.2s=\mathbf{14.4m}\)

Example Question #62 : Linear Motion And Momentum

A motorcycle accelerated from rest to \(\displaystyle 12\frac{m}{s}\)over a distance of 50 meters. What is the rider's acceleration?

Possible Answers:

\(\displaystyle a=2\frac{m}{s^2}\)

\(\displaystyle a=2.2\frac{m}{s^2}\)

\(\displaystyle a=.744\frac{m}{s^2}\)

None of these.

\(\displaystyle a=1.44\frac{m}{s^2}\)

Correct answer:

\(\displaystyle a=1.44\frac{m}{s^2}\)

Explanation:

To find the acceleration, use the kinematic equation \(\displaystyle v^2=V_{0}^2+2a(x-x_{0})\)

\(\displaystyle V_{f}=12\frac{m}{s}\)

\(\displaystyle V_{0}=0\)

\(\displaystyle (12\frac{m}{s})^2=2a(50m)\)

\(\displaystyle a=\frac{144\frac{m^2}{s^2}}{100m}=\boldsymbol{1.44\frac{m}{s^2}}\)

*the rider's acceleration will match that of the motorcycle.

Example Question #301 : Newtonian Mechanics

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 maximum height of the football.

Possible Answers:

\(\displaystyle 18.25m\)

\(\displaystyle 21.23m\)

None of these

\(\displaystyle 23.98m\)

\(\displaystyle 16.81m\)

Correct answer:

\(\displaystyle 21.23m\)

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:

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

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

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

The ball will be at it's maximum height when the \(\displaystyle y\) component of it's velocity, and thus that direction of kinetic energy, is zero.

The velocity will be decreased by the negative work done by gravity.

\(\displaystyle .5mv_y_i^2+mgh=.5mv_i_f^2\)

Plugging in values:

\(\displaystyle .5*20.4^2+(-9.8)h=.5*0^2\)

Solving for \(\displaystyle h\)

\(\displaystyle h=21.23meters\)

Example Question #62 : Motion In One Dimension

A projectile is fired at a wall with a speed of \(\displaystyle 400\frac{m}{s}\). It penetrates the wall to a distance of 0.053 meters before stopping. What is the acceleration of the projectile within the wall? Assume uniform acceleration.

Possible Answers:

\(\displaystyle a=5.11*10^6\frac{m}{s^2}\)

\(\displaystyle a=-1.51*10^6\frac{m}{s^2}\)

\(\displaystyle a=-5.11*10^6\frac{m}{s^2}\)

\(\displaystyle a=-2.51*10^6\frac{m}{s^2}\)

\(\displaystyle a=1.51*10^6\frac{m}{s^2}\)

Correct answer:

\(\displaystyle a=-1.51*10^6\frac{m}{s^2}\)

Explanation:

Use the kinematic equation \(\displaystyle V_{f}^2=V_{i}^2+2a(x-x_{0})\).

\(\displaystyle 0=(400\frac{m}{s})^2+2a(0.053m)\)

\(\displaystyle -160,000\frac{m^2}{s^2}=a(0.106m)\)

\(\displaystyle \frac{-160,000\frac{m^2}{s^2}}{0.106m}=a\)

\(\displaystyle \mathbf{a=-1.51*10^6\frac{m}{s^2}}\)

Negative acceleration because the projectile was slowing down.

Example Question #62 : Linear Motion And Momentum

A motorcycle must be traveling at \(\displaystyle 12\frac{m}{s}\) before leaving the end of a platform to clear a particular jump. If the motorcycle accelerates down the length of the ramp at \(\displaystyle 2.8\frac{m}{s^2}\) for 5 seconds will it clear the jump?

Possible Answers:

No, it will be moving \(\displaystyle 4\frac{m}{s}\) slower than necessary

No, it will be moving \(\displaystyle 2\frac{m}{s}\) slower than necessary

There is not enough information to determine

Yes, it will be moving \(\displaystyle 2\frac{m}{s}\) faster than necessary

Yes, it will be moving \(\displaystyle 4\frac{m}{s}\) faster than necessary

Correct answer:

Yes, it will be moving \(\displaystyle 2\frac{m}{s}\) faster than necessary

Explanation:

To find its speed before leaving the ramp,\(\displaystyle V_{f}=V_{0}+at\rightarrow 2.8\frac{m}{s^2}*5s=14\frac{m}{s}\).

Yes, it will be moving \(\displaystyle 2\frac{m}{s}\)faster than necessary. 

Example Question #341 : Ap Physics 1

You discover an old well in the forest behind your house. In order to ascertain its depth you drop a rock which falls straight down to the surface of the water. How deep is the well if it takes 5 seconds for the rock to hit the water (neglecting air resistance and the time it took for the sound to travel)? 

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

Possible Answers:

\(\displaystyle 75\hspace{1mm}m\)

\(\displaystyle 225\hspace{1mm}m\)

None of these

\(\displaystyle 154\hspace{1mm}m\)

\(\displaystyle 125\hspace{1mm}m\)

Correct answer:

\(\displaystyle 125\hspace{1mm}m\)

Explanation:

Use the kinematic equation \(\displaystyle \Delta x= x_{0}+v_{0}t+.5at^2\).

Since the object was dropped and starts at position 0 in the hand, the first two terms initial position and initial velocity become 0.

\(\displaystyle \Delta x=.5at^2 \rightarrow x=.5(10\frac{m}{s^2})(5)^2\rightarrow \boldsymbol{125 m}\)

Example Question #62 : Linear Motion And Momentum

A theme park ride raises the participants to a bird's eye view and then drops them. If it take 3 seconds for the ride to reach its stopping position below, what was the final speed before coming to a halt just above the ground? Ignore frictional forces.

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

Possible Answers:

\(\displaystyle V_{f}=6.2 \frac{m}{s}\)

\(\displaystyle V_{f}=62 \frac{m}{s}\)

\(\displaystyle V_{f}=3.11 \frac{m}{s}\)

\(\displaystyle V_{f}=31 \frac{m}{s}\)

\(\displaystyle V_{f}=311\frac{m}{s}\)

Correct answer:

\(\displaystyle V_{f}=31 \frac{m}{s}\)

Explanation:

Since the object is just falling it is only subject to the acceleration of gravity (especially since we are ignoring frictional forces).

So the final speed is equal to the time multiplied by the acceleration of gravity: \(\displaystyle V_{f}=10 \frac{m}{s^2}*3.1 s= \boldsymbol{31 \frac{m}{s}}\)

Example Question #68 : Motion In One Dimension

A man stands on a building \(\displaystyle 10m\) above the ground. He reaches over the side and throws an apple straight up with at a speed of \(\displaystyle 20\frac{m}{s}\)

How long does it take for the apple to hit the ground below?

Possible Answers:

\(\displaystyle 4.53s\)

\(\displaystyle 5.25s\)

\(\displaystyle 3.75s\)

\(\displaystyle 1.75s\)

\(\displaystyle 4.08s\)

Correct answer:

\(\displaystyle 4.53s\)

Explanation:

The apple is flying straight up with an initial velocity of \(\displaystyle 20\frac{m}{s}\), with the only force acting on it being gravity. Gravity will provide the apple with an acceleration of \(\displaystyle 9.8\frac{m}{s^2}\) directed downwards. The following kinematic equation is needed to solve for the time it takes for the apple to hit the ground:

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

The first step is to see how long it takes the apple to get to the highest point of its journey. At that point, the velocity will have slowed to zero:

\(\displaystyle v_i=20\frac{m}{s}\)

\(\displaystyle v_f=0\frac{m}{s}\)

\(\displaystyle a=-9.8\frac{m}{s^2}\)

Solving for t gives us:

\(\displaystyle t=\frac{v_f-v_i}{a}=\frac{0-20}{-9.8}=2.04 s\)

Since it took the apple 2.04 seconds to get to the top, that means it will take the apple another 2.04 seconds to get back to its starting point. This also means that the velocity of the apple when it reaches is starting point will be equal and opposite its starting velocity:

\(\displaystyle v_f=v_i+a*t=0-9.8(2.04)=-20\frac{m}{s}\)

To find the amount of time it takes the apple to reach the ground, the following kinematic equations are used:

\(\displaystyle v_f^2=v_i^2+2ad=-20^2+2*-9.8*-10=596\frac{m^2}{s^2}\)

\(\displaystyle v_f=\sqrt596=24.41\frac{m}{s}\)

And:

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

\(\displaystyle t=\frac{v_i-v_f}{a}=\frac{-20+24.41}{9.8}=0.45s\)

Therefore, the total time it takes for the apple to reach the ground is:

\(\displaystyle t_{total}=t_1+t_2+t_3=2.04+2.04+0.45=4.53s\)

Example Question #301 : Newtonian Mechanics

Mark, Jim, and David apply forces to an object of mass \(\displaystyle 3 kg\). The object is on level ground where the coefficient of friction is \(\displaystyle .3\). Mark applies a \(\displaystyle 40N\) force to the right, Jim applies a \(\displaystyle 3N\) force to the left, and David applies a \(\displaystyle 3 N\) force down. How far will the object travel (in meters) after \(\displaystyle 4\) seconds? Assume it starts at rest and the coefficient of static friction is low enough for the object to start moving with the mentioned forces.

Possible Answers:

\(\displaystyle 72m\)

\(\displaystyle 98.67m\)

\(\displaystyle 10.67m\)

\(\displaystyle 33m\)

\(\displaystyle 9m\)

Correct answer:

\(\displaystyle 72m\)

Explanation:

We can split this question up into the x-direction and y-direction. In the y-direction, the object's acceleration is zero since it's going to remain in contact with the ground. We now can write our \(\displaystyle \sum F=ma\) equation (let the up direction be positive). Since it's not accelerating, we have

\(\displaystyle \sum F=ma=0\rightarrow F_{n}-mg-3=0\)

\(\displaystyle F_{n}\) denotes the normal force. We know that the mass is \(\displaystyle 3kg\) and that \(\displaystyle g\approx10\frac{m}{s^2}\), so we can solve for the normal force, which we'll later use to find the force of friction. \(\displaystyle F_{n}-(3kg)(10\frac{m}{s^2})-3=0\)

\(\displaystyle F_{n}=33N\)

The force of friction \(\displaystyle (F_{f})\) is equal to \(\displaystyle \mu F_{n}\) (where \(\displaystyle \mu\) denotes the coefficient of friction), so

\(\displaystyle F_{f}=(.3)(33N)=9.9N\)

In the x-direction, we'll denote right as positive. The forces in the x-direction are \(\displaystyle 40N\) right, \(\displaystyle 3N\) left, and \(\displaystyle 9.9N\). Now we can write our \(\displaystyle \sum F=ma\) equation as \(\displaystyle 40N-3N-9.9N=(3kg)a\)

\(\displaystyle \frac{27.1N}{3kg}=9.0\frac{m}{s^2}\)

Using this acceleration, we can use kinematics to solve for the distance the object will travel in \(\displaystyle 4\) seconds. We have time and acceleration, but we need distance, so we'll use the equation: \(\displaystyle x(t)=(v_{initial})t+0.5at^2\)

\(\displaystyle v_{initial}=0\)

 \(\displaystyle x=0.5(9.0\frac{m}{s^2})(4s)^2=72m\)

Learning Tools by Varsity Tutors