# Rotational Motion - Help me out GUYS

• dagg3r
In summary, rotational motion is the movement of an object around an axis or center point in a circular path. It is different from linear motion, which is movement in a straight line. Torque is a measure of the force that causes rotational motion, and angular velocity is the rate at which an object rotates around an axis. Rotational motion is used in various real-life applications, from the rotation of wheels on a car to the movement of machines and devices such as engines and turbines.
dagg3r
hi guys i got a couple of questions can somebody help me out by telling me the steps of where to go about and i will try to get the answer on my own as i need to understand how to do these questions i will post what i know.

1. a train slows down as it turns, from 90 km/hr to 50 km/hr in 15seconds. the radius is 150m, calculate the acclereation the moment it reaches 50km/hr.

first of all i know the formula is a= v^2 / r
what i don't know is that i am given 90k/hr and 50 km/hr, time and a radius, I am thinking maybe i don't use the a=v^2/r formula but perhaps v= u + at ?

2. there is a pictuer of a circle all i am given is radius is 2.50 m, outside the circle is a= 15 m/s^2 and insie the circle is an angle of 30degrees with a line going down. It wants me to calculate radial, tangential accerlearation along with the speed of the particle.

im thinking maybe the a=15 m/s^2 is the overall accleration and maybe use the components of sin30 and cos30 I am lost please shed me some light ppl thanks

dagg3r said:
1. a train slows down as it turns, from 90 km/hr to 50 km/hr in 15seconds. the radius is 150m, calculate the acclereation the moment it reaches 50km/hr.

first of all i know the formula is a= v^2 / r
what i don't know is that i am given 90k/hr and 50 km/hr, time and a radius, I am thinking maybe i don't use the a=v^2/r formula but perhaps v= u + at ?

You are in the right track. You find the centripetal acceleration as a = v^2/r and tangential acceleration as a = v-u/t. Add them as vectors and you will get the net acceleration.

dagg3r said:
2. there is a pictuer of a circle all i am given is radius is 2.50 m, outside the circle is a= 15 m/s^2 and insie the circle is an angle of 30degrees with a line going down. It wants me to calculate radial, tangential accerlearation along with the speed of the particle.

im thinking maybe the a=15 m/s^2 is the overall accleration and maybe use the components of sin30 and cos30 I am lost please shed me some light ppl thanks

As far as I get it, you're given the net acceleration a of a particle at the edge of the wheel of radius r, crossed by a radial line forming 30degrees with the vertical. So you are asked to find the radial and tangential accelerations of that particle. But still you would need the speed of the wheel.

For the first question, you are correct in thinking that the formula a=v^2/r may not be the most appropriate in this case. Instead, you can use the formula a=(vf-vi)/t, where vf is the final velocity (50 km/hr), vi is the initial velocity (90 km/hr), and t is the time (15 seconds). This will give you the acceleration of the train as it slows down.

To find the tangential and radial acceleration in the second question, you can use the equations at=ar=ω^2r and at=ωr, where ω is the angular velocity. You can calculate the angular velocity using the formula ω=v/r, where v is the speed of the particle. Then, use trigonometry to find the components of the acceleration in the radial and tangential directions.

I hope this helps shed some light on the problems. Remember to always carefully read the given information and use the appropriate formulas to solve the problems. Keep practicing and you will get the hang of it! Good luck!

## 1. What is rotational motion?

Rotational motion is the movement of an object around an axis or center point, where every point on the object moves in a circular path.

## 2. What is the difference between linear and rotational motion?

Linear motion is the movement of an object in a straight line, while rotational motion is the movement of an object around an axis. Linear motion can be described by displacement, velocity, and acceleration, while rotational motion can be described by angular displacement, angular velocity, and angular acceleration.

## 3. What is torque and how does it relate to rotational motion?

Torque is a measure of the force applied to an object to cause it to rotate. It is calculated by multiplying the force applied by the distance from the axis of rotation. In rotational motion, torque is responsible for causing objects to rotate around an axis.

## 4. What is angular velocity and how is it calculated?

Angular velocity is the rate at which an object rotates around an axis. It is calculated by dividing the change in angular displacement by the change in time. It is measured in radians per second (rad/s).

## 5. How is rotational motion used in real-life applications?

Rotational motion is used in many real-life applications, such as the rotation of wheels on a car, the spinning of a top, and the movement of a Ferris wheel. It is also used in machines and devices that require rotational movement, such as engines, turbines, and motors.

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