Question

Consider a car travelling at 60 km/hr. If the radius of a tire is 25 cm, calculate the angular speed of a point on the outer edge of the tires. If the car takes 6 seconds to come to a stop, calculate the average angular acceleration of a point on the outer edge of the tires.
A.-0.11 rad/s 2
B. -40.0 rad/s 2
C. -2.78 rad/s^2
D. 11.1 rad/s 2

Jack and Jill have made up since the previous HW assignment, and are now playing on a 10 meter seesaw. Jill is sitting on one end of the seesaw, while Jack is some distance (d) from the fulcrum on the other side. If Jack and Jill have masses of 100 kg and 60 kg, respectively, where should Jack sit in order to balance the seesaw?

A. 8 m from the fulcrum
B. 3 m from the fulcrum
C. Not enough information.
D. 5 m from the fulcrum

Answer 1

Answer

given,

speed of car = 60 km/hr

                     = 60 x 0.278 m/s

                     = 16.68 m/s

radius of the tire = 25 cm = 0.25 m

time taken to stop = 6 s

average acceleration = ?

$\omega = \dfrac{v}{R}$

$\omega = \dfrac{16.68}{0.25}$

$\omega =66.72 rad/s$

average acceleration= $\dfrac{\Delta \omega}{\Delta t}$

                                   =  $\dfrac{66.72}{6}$

                                   = 11.12 rad/s²

correct answer option D

b) length of sea saw = 10 m

mass of jack = 100 Kg

mass of Jill = 60 Kg

Let y be the distance from the Jack. To balance the seesaw moment on both side should balance each other about fulcrum

   now,

     100 x y = 5 x 60

             y = 3 m

the correct answer is option B