Spinning frisbee

I spin a frisbee on my finger about the center of the frisbee. I then hit the side of the frisbee to make it spin twice as fast as originally. By what factor has the kinetic energy of the frisbee increased?


The answer is 4.

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11 solutions

By formula of K. E. ,K. E is directly proportional to square of velocity since velocity is doubled As given Kinetic energy is quadruple

thx

Kou$htav Chakrabarty - 7 years, 7 months ago

^Note that while this is correct, the mass is also factored in - K.E. is directly proportional to m v 2 mv^2 . However, this does not affect the situation in this problem, as the mass stays constant.

William Cui - 7 years, 7 months ago

its rotational k.e =half*moment of inertia * angular velocity^2 .

4 times is ans

Abhishek Mishra - 7 years, 7 months ago

I have used same logic !

Devesh Rai - 7 years, 6 months ago

please explain why K .E=1/2 Mv*v

Debjyoti Chattopadhyay - 7 years, 6 months ago
William Cui
Nov 13, 2013

The formula for kinetic energy is K E = 1 2 m v 2 KE = \frac{1}{2} \cdot m \cdot v^2 , where m m represents the mass and v v represents the the velocity of the object (in this case, the frisbee)

The frisbee's mass stays constant (it doesn't get heavier or lighter while it is being spun), while the velocity doubles when it is being spun at the side, as given in the problem.

Since the velocity doubles and the rest of the terms stay the same, the factor of the kinetic energy is increased by v 2 = 2 2 = 4 v^2=2^2=\boxed{4} .

Budi Utomo
Dec 24, 2013

Because Velocity have square so if the ratio is 2 so, increase 2^2 = 4

Michael Tang
Dec 18, 2013

Since E = 1 2 m v 2 , E = \dfrac12mv^2, increasing the velocity by a factor of 2 2 increases the kinetic energy by a factor of 2 2 = 4 . 2^2 = \boxed{4}.

Raja Fakirchandra
Nov 11, 2013

we have

E = (1/2)mv2

now if 'v' is doubled the kinetic energy will be

E' = (1/2)m.(2v)2

= 4.[(1/2)mv2]

so,

kinetic energy will become four times.

http://www.meritnation.com/ask-answer/question/i-spin-a-frisbee-on-my-finger-about-the-center-of-the-frisbe/motion-in-a-plane/4971513 ;)

Sherif Elmaghraby - 7 years, 6 months ago
Asif Iqbal
Mar 9, 2014

4 times

Chibueze Elisha
Nov 17, 2013

k.e1 = 1/2mv^2; frisbee spins twice as fast, therefore, velocity increases by a factor of 2; k.e2 = 1/2m(2v)^2 = 4 x 1/2mv^2; hence kinetic energy increases by a factor of 4

Mansoor Khan
Nov 14, 2013

it means kinetic energy increases 4 times

Waqar Zaman
Nov 14, 2013

since K.E=(0.5) m v^2 and when speed become double of original speed then v=2v so, K.E=(0.5) m(2v)^2=(0.5) m 4v^2 =4 K.E

.

Vishnu Agrawal
Nov 12, 2013

we have 1/2mv^2 we've been given v=2times therefore4[1/2mv^2]

Hamid Yasir
Nov 10, 2013

we have E = (1/2)mv2 now if 'v' is doubled the kinetic energy will be E' = (1/2)m.(2v)2 = 4.[(1/2)mv2] so, kinetic energy will become four times.

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