IIT JEE , AIEEE Forum - Physics , Mechanics

nancy_shrija

1.a sphere cant roll on

a. smooth horizontal surface b.smooth inclined surface

c. rough horizontal surface d.rough inclined surface

(confused between a & b.shouldn't both be correct?)

2.angular velocity of engine of a scooter is propotonal to the petrol input per second.the scooter is moving on a frictionless road with uniform velocity.if petrol input is increased by 10%,the linear velocity of the scooter is increased by

a.80% b.10% c. 20% d.0%

nishant_88

i guess no 2 should be 10% because angular velocity is proportional to linear velocity as radius is constant.
So linear velocity is proportional to petrol input.

Please correct me if I am wrong.

nirmal123

b is the answer

vidyun_dusa

2) d) the velocity remains unaltered as the road is frictionless

waterdemon

No you all are messing it up.

The road is completely frictionless so the friction offered

by the road to the scooter is not enough for the scooter

to increase its Angular velocity.

Since acceleration is not changing therefore dv/dt = 0

Therefore Even if the "input" of oil is increased by 10%

even then there is no change in linear velocity.

Ans:Option (d) as per me 0%.

plZ rate if correct.

Cheers!!!!!!!@@@!!!!!!!!!

gomurali

on smooth horizontal surface, rolling will not be produced only sliding will be produced. The answer must be rough inclined plane. Because sufficient friction must be there for the rolling to take place

hiran

Rolling starts when the the point in contact with the ground is at instantaneous rest. This happens only when two opposing forces say, The force f with which the ball is moving and the frictional force which opposes motion, act on it thus making net force zero. So, answers are c and d.

nancy_shrija

hiran,

basically the question is 'sphere can not roll on" and the options follow.so according to u both a & b are right?(which even i feel but only b is the right option)

gomurali

ya answer a and b

iitkgp_bipin

In pure rolling the point of contact is at rest. To make it happen there should be a frictional force acting on the body on the surface.

Hence a sphere cant roll on any smooth plane.

Betu

sphere can't roll on smooth horizontal surface....because the friction at the point of contact which provides the torque to roll is zero.

But sphere can roll on smooth inclined surface as the torque will provided by its weight around the point of contact. (i'm poor at drawing the diagram otherwise i'd have shown it to further clarify.

hence answer is a) and not b)

2nd question..

i wonder whether scooter can rollon smooth surface....so initially also no angular velocity..scooter can only skid..!!!!!

Betu

bipin..pure rolling needs point of contact to be at rest....but sphere can roll & skid simultaneusly ...question is about rolling only....not pure rolling

MUDIT

ABOUT THE PROBLEM OF ROTATION OF THE SPHERE, I FEEL THAT OPTIONS A AND B BOTH SHOULD BE CORRECT. BUT IF A CHOICE HAS TO BE MADE THEN I WOULD GO FOR OPTION B. IF A SPHERE IS KEPT ON A HORIZONTAL SURFACE, THEN, IF THE FORCE IS APPLIED ANY WHERE EXCEPT AT A LINE JOINING TO ITS CENTRE PURE ROTATION IS POSSIBLE. THE FORCE WOULD PROVIDE TORQUE AS WELL AS FORCE. BUT IF THE SPHERE IS KEPT ON A INLCINED PLANE COMPONENT OF Mg WOULD BE ACTING FROM THE CENTRE. SO YOU WOULD REQUIRE AN EXTRA COMPARABLE FORCE TO PROVIDE THE NECESSARY TORQUE
CORRECT ME IF I AM WRONG

nancy_shrija

betu

the answer for the question is (b) and not (a)

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