MCAT Physical : MCAT Physical Sciences

Study concepts, example questions & explanations for MCAT Physical

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Example Questions

Example Question #281 : Mcat Physical Sciences

A cannon fires a cannon ball at an angle of 60o relative to the ground. The cannon ball comes out at an initial velocity of . Assume there is no air resistance.

How long will the cannon ball stay in the air?

Possible Answers:

Correct answer:

Explanation:

In order to solve for the amount of time, we need to know the vertical initial velocity of the cannonball. This is given by the equation . Using the initial velocity of  we determine that the vertical initial velocity is 

Knowing this, we can solve the amount of time it will take for the cannon ball to reach its maximum peak, with a velocity of  using the equation 

This is the amount of time it takes for the ball to reach its peak, not the total time it is in the air. Since the ball must drop from the maximum height, we double the time and arrive at the correct answer of 20.8s.

Example Question #102 : Newtonian Mechanics And Motion

A cannon fires a cannon ball at an angle of 60o relative to the ground. The cannon ball comes out at an initial velocity of . Assume there is no air resistance.

Which of the following statements is true?

Possible Answers:

The vertical velocity of the cannon ball changes during its flight

The horizontal velocity of the ball changes during its flight

The acceleration of the ball changes during its flight

None of these vectors change during the ball's flight

Correct answer:

The vertical velocity of the cannon ball changes during its flight

Explanation:

The only acceleration on the cannon ball is done by gravity, which is constant throughout the ball's flight. Since there is no air resistance, the horizontal velocity of the ball is also constant, however, the vertical velocity of the ball is not constant, because the velocity of the ball changes throughout its flight.

It is  at the beginning ()and is  at the maximum height of the cannon ball.

Example Question #1 : Motion In Two Dimensions

An object is shot from the ground at 75m/s at an angle of 45⁰ above the horizontal. How high does the object get before beginning its descent?

Possible Answers:

140m

280m

70m

420m

Correct answer:

140m

Explanation:

The velocity must be broken down into x (horizontal) and y (vertical) components. We can use the y component to find how high the object gets. To find vertical velocity, vy, use .

Next we find how long it takes to reach the top of its trajectory using .

 t = 5.3s

Finally, find how high the object goes with .

 

Example Question #1 : Motion In Two Dimensions

An object is shot from the ground at 125m/s at an angle of 30o above the horizontal. How far away does the object land?

Possible Answers:

250m

62.5m

675m

1350m

Correct answer:

1350m

Explanation:

First, find the horizontal (x) and vertical (y) components of the velocity

Next, find how long the object is in the air by calculating the time it takes it to reach the top of its path, and doubling that number.

t = 6.25s 

Total time in the air is therefore 12.5s (twice this value).

Finally, find distance traveled my multiplying horizontal velocity and time.

Example Question #2 : Motion In Two Dimensions

A 2kg box is at the top of a frictionless ramp at an angle of 60o. The top of the ramp is 30m above the ground. The box is sitting still while at the top of the ramp, and is then released.

What is the velocity of the box just before it hits the ground?

Possible Answers:

Correct answer:

Explanation:

We can start this problem by determining how much time it takes the box the reach the ground. Since the vertical distance is 30m and we know the angle of the ramp.

Now that we have the distance traveled, we can determine the acceleration on the box due to gravity, using the equation .

We can plug these values into the following distance equation and solve for time.

Now that we know the acceleration on the box and the time of travel, we can use the equation  to solve for the velocity.

Example Question #2 : Motion In Two Dimensions

A 2kg box is at the top of a frictionless ramp at an angle of . The top of the ramp is 30m above the ground. The box is sitting still while at the top of the ramp, and is then released.

When the box is released, how long will it take the box to reach the ground?

Possible Answers:

Correct answer:

Explanation:

We can start this problem by determining how far the box will travel on the ramp before hitting the ground. Since the vertical distance is 30m and we know the angle of the ramp, we can determine the length of the hypotenuse using the equation .

Now that we have the distance traveled, we can determine the acceleration on the box due to gravity. Because the box is on a sloped surface, the box will not experience the full acceleration of gravity, but will instead be accelerated at a value of . Since the angle is 60o, the acceleration on the box is  

Finally, we can plug these values into the following distance equation and solve for time.

 

Example Question #11 : Gre Subject Test: Physics

A cannon fires a cannon ball at an angle of  relative to the ground. The cannon ball comes out at an initial velocity of . Assume there is no air resistance.

How far will the ball be from the cannon once it hits the ground?

Possible Answers:

Correct answer:

Explanation:

We must first determine the amount of time that the ball is in the air, then use the horizontal velocity to solve for the distance travelled.

In order to solve for the amount of time, we need to know the vertical initial velocity of the cannonball. This is given by the equation . Using the initial velocity of  we determine that the vertical initial velocity is 

Knowing this, we can solve the amount of time it will take for the cannon ball to reach its maximum peak, with a velocity of  using the equation 

This is the amount of time it takes for the ball to reach its peak, not the total time it is in the air. Since the ball must drop from the maximum height, we double the time and find that total flight time is 20.8s.

The next step is determining the horizontal initial velocity from the cannon. This is determined using the equation below.

Since we assume that there is no air resistance, we can conclude that the horizontal velocity of the cannonball will remain constant throughout its flight. As a result, the total displacement equation is simplified to the following: .

Example Question #12 : Motion In Two Dimensions

A 2kg lead ball is loaded into a spring cannon and the cannon is set at a 45º angle on a platform. The spring has a spring constant of 100N/m and the ball and spring system is compressed by 1m before launch. While the ball is in flight air resistance can be neglected, and the ball finishes its flight by landing at a cushion placed some distance away from the cannon.

How high does the ball fly?

Possible Answers:

2.57m

8.50m

5.69m

4.91m

Correct answer:

2.57m

Explanation:

First, solve for the initial vertical velocity of the ball.

vy = (10m/s)(sin(45o)) = 7.1m/s

Think back to the 3 main kinematics equations we know:

vf2 = vi2 + 2aΔx

vf = vi + at

Δx = vit + ½at2

We need to choose an equation that allows us to solve for the vertical height of the ball, given that we know the initial vertical velocity, final vertical velocity (zero), and the acceleration due to gravity (-9.8m/s2).

vf2 = vi2 + 2aΔy

Δy = (vf2 - vi2)/2a

Example Question #113 : Newtonian Mechanics And Motion

A 2kg lead ball is loaded into a spring cannon and the cannon is set at a 45º angle on a platform. The spring has a spring constant of 100N/m and the ball and spring system is compressed by 1m before launch. While the ball is in flight air resistance can be neglected, and the ball finishes its flight by landing at a cushion placed some distance away from the cannon.

How long does it take for the ball to land on the cushion?

Possible Answers:

1.12s

1.44s

3.40s

0.72s

Correct answer:

1.44s

Explanation:

Once again, think back to our 3 main kinematics question:

vf2  = vi2 + 2aΔx

vf = vi + at

Δx = vit + ½at2

We want an equation that allows us to determine the time the ball spends in flight. Often, it is easier to compute the time it takes for the ball to reach its maximum height, then multiply by two. However, this “shortcut” only works when the launch point and end point are at the same vertical height, as they are in this problem.

vf = vi + at

t = (vf – vi)/a

Remember to use the veritcal velocity as your initial velocity.

vy = (10m/s)(sin(45o)) = 7.1m/s

This is one half of the flight time. We multiply by two to find the total time.

t = 2(0.72s) = 1.44s

Example Question #283 : Mcat Physical Sciences

A 2kg lead ball is loaded into a spring cannon and the cannon is set at a 45º angle on a platform. The spring has a spring constant of 100N/m and the ball and spring system is compressed by 1m before launch. While the ball is in flight air resistance can be neglected, and the ball finishes its flight by landing at a cushion placed some distance away from the cannon.

In order to catch the ball in the center of the cushion, how far away should the cushion be placed?

Possible Answers:

7.8m

2.9m

10.2m

11.0m

Correct answer:

10.2m

Explanation:

First, we will need the time that the ball is in flight.

Think back to our 3 main kinematics question:

vf2  = vi2 + 2aΔx

vf = vi + at

Δx = vit + ½at2

We want an equation that allows us to determine the time the ball spends in flight. Often, it is easier to compute the time it takes for the ball to reach its maximum height, then multiply by two. However, this “shortcut” only works when the launch point and end point are at the same vertical height, as they are in this problem.

vf = vi + at

t = (vf – vi)/a

Remember to use the veritcal velocity as your initial velocity.

vy = (10m/s)(sin(45o)) = 7.1m/s

This is one half of the flight time. We multiply by two to find the total time.

t = 2(0.72s) = 1.44s

Using this time with the initial horizontal velocity will allow us to solve for the total horizontal distance.

 vx = (10m/s)(cos(45o)) = 7.1m/s

Δx = vit + ½at2

Δx = (7.1m/s)(1.44s) = 10.22m

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