Rotational Motion - Help me out GUYS

[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

 

[ramollari]

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.

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.

 

[thepatientmental]

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!