# Kinematics Problem (Find Speed)

• airking95
In summary, the daredevil motorcyclist needs to have a minimum speed of 15.4 m/s, launched at a 15 degree angle, in order to clear the 48m wide gorge with a vertical height difference of 5.9m below the launching point. This can be solved by understanding projectile motion, knowing about vectors and their operations, and remembering or deriving SUVAT equations.
airking95

## Homework Statement

A daredevil motorcyclist attempts to leap a 48m wide gorge. At the side where the cyclist starts, the ground slopes upward at an angle of 15 degrees. Beyond the far rim, the ground is level and is 5.9m below the near rim. what is the minimum speed necessary for the cyclist to clear the gorge?

## Homework Equations

Kinematics Equations

s=d/t
d= vf(t)-0.5(a)(t)2

## The Attempt at a Solution

First I just used Pythagorean therm to find Δd. 482+5.92= c2

c= 48.36

Used equation to find time

Δd = VfΔt-0.5(a)Δt2
48.36= -0.5(-9.8)Δt2
48.36 = 4.9Δt2
48.36/4.9=Δt2
9.86 =Δt2
+ - 3.14 = Δt

s=d/t
s=48.36/3.14
s=15.4 m/s

I think I was suppose to do something with 15 degrees.

I got the answer as 15 m/s, but I believe its wrong.

Last edited:
Maybe you show us your workings and if we can spot any errors you might have made.

azizlwl said:
Maybe you show us your workings and if we can spot any errors you might have made.
First I just used Pythagorean therm to find Δd. 482+5.92= c2

c= 48.36

Used equation to find time

Δd = VfΔt-0.5(a)Δt2
48.36= -0.5(-9.8)Δt2
48.36 = 4.9Δt2
48.36/4.9=Δt2
9.86 =Δt2
+ - 3.14 = Δt

s=d/t
s=48.36/3.14
s=15.4 m/s

I think I was suppose to do something with 15 degrees.

1. Why vf=0?
2. The vertical height difference 5.9m below the launching point.

azizlwl said:
1. Why vf=0?
2. The vertical height difference 5.9m below the launching point.

How do I solve it without putting Vf as 0, and yes the vertical height difference is 5.9m below the launching point.

$\vec {A}=\vec {B}+\vec {C}$

The motorcyle launches at 15° above the ground.
Since it is vector in 15° direction, you can resolved it to 2 components.
Y direction which affected by gravity and a constant X direction.

azizlwl said:
$\vec {A}=\vec {B}+\vec {C}$

The motorcyle launches at 15° above the ground.
Since it is vector in 15° direction, you can resolved it to 2 components.
Y direction which affected by gravity and a constant X direction.

Can you please show me, how you would solve this please ??

If you do it once in lifetime, it is useful in giving you the answer.
I'll only tell you what prequisite knowledge that you should acquire in order to solve this type of question.

If you want to do physics problems, you should know about vectors and its operations.
Secondly you should know/remember/derive(this makes you less equations to remember) SUVAT equations.

This is a projectile motion problem. What can you tell us about projectile motion? What equations do you have that apply to projectile motion?

If you have a question why we need vector components, then you are on the way to solve the problem.
http://imageshack.us/a/img805/2684/20946647.jpg

Last edited by a moderator:
I'm really really sorry to hijack, but just wondering, is the answer 21.75m/s? Attempted it as practice, and just want to check the answer if I made any errors. Sorry! And Thanks!

Nope. I get v0=25.4 m/s.

Okay thanks lots! Time to redo then... :/

## 1. What is kinematics?

Kinematics is a branch of physics that deals with the motion of objects without considering the forces that cause the motion.

## 2. How do you find speed in a kinematics problem?

To find speed in a kinematics problem, you need to know the distance an object has traveled and the time it took to travel that distance. You can then use the formula speed = distance/time to calculate the speed.

## 3. What is the difference between speed and velocity in kinematics?

Speed is the rate at which an object is moving, while velocity is the speed and direction of an object's motion. In other words, velocity takes into account the direction of movement, while speed does not.

## 4. How can you represent the motion of an object in a kinematics problem?

The motion of an object in a kinematics problem can be represented using a position-time graph, a velocity-time graph, or an acceleration-time graph. These graphs show the changes in an object's position, velocity, and acceleration over time.

## 5. What are some common units of measurement used in kinematics?

The most common units of measurement used in kinematics are meters (m) for distance, seconds (s) for time, and meters per second (m/s) for speed and velocity. Acceleration is typically measured in meters per second squared (m/s^2).

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