# Homework Help: Linear and Angular Motion Help

1. Oct 26, 2014

### JohnP60

1. The problem statement, all variables and given/known data
Need a bit off help with these questions would appreciate some help.

2. Relevant equations
1. An accelerating vehicle crosses a datum with a velocity of 20m/s and then covers a distance of 2.5km in 50s. Calculate the acceleration, and the velocity reached after it has travelled 2.5km.

2. If a rotor is rotating at 2000 rev/min accelerates to 3000 rev/min in 6 seconds calculate its acceleration and angle turned through.

3. Calculate the velocity of a belt in a belt drive system where the pulley is 82.3cm diameter and rotates at:
a) 1750 rev/min
b) 40 rev/s

3. The attempt at a solution
1. a=v-u / t
20/50 = 0.4m/s^2

v=u+at
20 + 0.4 x 50 = 40m/s

2. 314.16 - 209.43 / 6 = 17.5 rad/s^2

w= wo t + 1/2 a t^2
1256.58 + 315

3. Unsure how to do this one

Thanks

2. Oct 26, 2014

### Staff: Mentor

This assumes the velocity changes by 20m/s in 50 seconds. You don't know if that is true.
Simple cross-check: if the vehicle drives with a speed between 20m/s and 40m/s, in 50s it cannot go further than 40m/s*50s = 2km. Certainly not 2.5km.
Checks like those are useful to see if your answer can make sense.
There are missing brackets, but this problem will vanish with proper fractions on paper.

3. The pulley is a circle, the belt is moving at the outer edge with the same speed as this outer edge.

3. Oct 26, 2014

### JohnP60

Unsure what you mean with Q1. Am i using wrong formulas?

a)V=Rw
0.41x183.26
=75.14m/s

b)V=Rw
0.41x251.33
=103.04m/s

4. Oct 26, 2014

### Staff: Mentor

Yes.

3 looks good.

As a general remark, it is easier to understand what you are doing if you start with a formula, and with the values given in the problem statement.