# Help with one 2-D kinematics problem? Answer is off by 2

• RyanJF
In summary, the problem involves a motorcycle daredevil attempting to jump over as many buses as possible. The takeoff ramp has an 18 degree angle and the landing ramp is identical. Each bus is 2.74 m wide and the cyclist has a speed of 33.5 m/s. Using kinematics equations, the maximum number of buses he can jump is calculated to be 26.65, but the answer in the book is 24, indicating a possible error. The student is seeking clarification and verification of their approach.
RyanJF

## Homework Statement

"A motorcycle daredevil is attempting to jump across as many buses as possible. The takeoff ramp makes an angle of 18 degrees above the horizontal, and the landing ramp is identical to the takeoff ramp. The buses are parked side-by-side, and each bus is 2.74 m wide. The cyclist leaves the ramp with a speed of 33.5 m/s. What is the maximum number of buses over which the cyclist can jump?"

A = 9.8

## Homework Equations

Kinematics equations

## The Attempt at a Solution

First thing I knew I had to do was find the original velocity in the X-component. To solve for this, I did:

Vx = Cos18 * 33.5 = 31.86 m/s
Vx, Vox = 31.86 m/s

In order to use a distance equation, I knew that it was necessary to solve for time. I used the following equation, substituting overall distance with the distance of one bus:

T = sqrt(2x/a)

T = sqrt(2*2.74/9.8)

T = .75 sec

Then I selected one of the kinematics equations for distance in the x:

Xx = VoxT + 1/2 * 9.8 * t^2

Xx = (31.86 * .75) + 1/2 * 9.8 * .75^2

Xx = 26.65

I assumed that since "T" represented the time it took to jump one bus, that the numerical conclusion of the above equation would equal the number of buses able to be jumped by the daredevil.

However, the "answer section" in the back of the book says that the cyclist can jump only 24 buses, which would be 2-3 buses less than what I got, depending on which way you decided to round.

Can somebody please show me what I'm doing wrong? I have a test tomorrow and while I don't like to blame things on the teacher, a lot of people have been saying that he doesn't explain things too thoroughly, and I'd prefer to keep my 100%.

EDIT:

I've been trying to learn this from the book. The only review we got from the teacher were a bunch of really irrelevant questions.

I don't know whether or not my answer is still incorrect, but I've realized that results presented in my book do not match up with results presented by my calculator - I was working through an example problem, and I'm quite sure that the work done in the book was not right... =\

Or maybe my calculator is messed up. One of the two.

## What does "Help with one 2-D kinematics problem? Answer is off by 2" mean?

This phrase likely refers to a physics problem involving motion in two dimensions (2-D) that requires assistance and has an answer that is two units or values off from the correct solution.

## What is kinematics?

Kinematics is the branch of physics that studies the motion of objects without considering the forces that cause the motion.

## How do I approach a 2-D kinematics problem?

To solve a 2-D kinematics problem, you first need to identify the given information and what you are trying to solve for. Then, use the appropriate equations for displacement, velocity, and acceleration in both the x and y directions to solve the problem step by step.

## What are some common mistakes when solving 2-D kinematics problems?

Some common mistakes include mixing up the x and y components, using the wrong equation, and not considering the direction of the motion. It is also important to pay attention to units and conversions.

## How can I improve my understanding of 2-D kinematics?

Practicing various types of 2-D kinematics problems and seeking help from a teacher or tutor can improve understanding. It is also helpful to have a strong understanding of basic concepts such as displacement, velocity, and acceleration in one dimension before tackling 2-D problems.

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