Deduce The Weight Of This Frog

Image source: Mudfooted.com

A frog is jumping around a pond. At some time t t , the frog is in the air and has a kinetic energy of 1 J 1~\mbox{J} and a momentum of magnitude 0.5 kg m/s 0.5~\mbox{kg}\cdot\mbox{m/s} . What is the mass of the frog in kg ?


The answer is 0.125.

This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try refreshing the page, (b) enabling javascript if it is disabled on your browser and, finally, (c) loading the non-javascript version of this page . We're sorry about the hassle.

15 solutions

Andhika Rahardian
Oct 28, 2013

from the question we know that ,

p = 0.5 k g p=0.5 kg m / s m/s or we can change to \Rightarrow m v = 0.5 k g mv= 0.5 kg m / s m/s

1 2 m v 2 = 1 J \frac {1}{2} mv^{2}= 1 J \Rightarrow kinetic energy = 1 2 m v 2 \frac {1}{2} mv^{2}

m v 2 = 2 J mv^{2} = 2 J

m v × v = 2 J mv \times v = 2J

back to the top, cause m v = 0.5 k g mv = 0.5 kg m / s m/s so we can write

0.5 k g 0.5 kg m / s × v = 2 J m/s \times v =2J \Rightarrow v = v= 4 4 m / s m/s

substitute v = v= 4 4 m / s m/s to \Rightarrow m v = 0.5 k g mv = 0.5 kg m / s m/s

m × 4 m \times 4 m / s = 0.5 k g m/s = 0.5 kg m / s m/s

m = 0.125 k g m = \boxed {0.125} kg

Note : m v = m a s s × v e l o c i t y mv = mass \times velocity

m / s m/s = = meter per second or velocity

1 Joule Equals 1 k g m 2 s 2 1 \frac {kg * m^{2}}{s^{2}}

Good answer !

Pham Tung - 7 years, 7 months ago
Priyansh Sangule
Oct 28, 2013

Okay .

We know that :

K i n e t i c e n e r g y = m v 2 2 = 1 J Kinetic energy = \dfrac{mv^2}{2} = 1 J

And that :

M o m e n t u m = m v = 0.5 k g m / s Momentum = mv = 0.5 kg \cdot m/s

Therefore , by manipulating the formula for KE (i.e Kinetic energy) ,

m v 2 2 = 1 \dfrac{mv^2}{2} = 1

1 2 ( m v ) v = 1 \Rightarrow \dfrac{1}{2} \cdot (mv) \cdot v = 1

1 2 ( 0.5 ) v = 1 \Rightarrow \dfrac{1}{2} \cdot (0.5) \cdot v = 1

v = 4 \Rightarrow v = 4

Putting v = 4 v = 4 in the formula for momentum ,

We get m v = m 4 = 1 2 mv = m \cdot 4 = \dfrac{1}{2}

m = 1 8 = 0.125 \Rightarrow m = \dfrac{1}{8} = \boxed{0.125}

nice solution

Devesh Rai - 7 years, 7 months ago
Shiemka Juson
Jan 8, 2014

P = 0.5 kg m/s

KE = 1 J

KE = (1/2)mv^2

P = mv

substituting equation for momentum into equation for kinetic energy...

KE = (1/2)(P/m)^2

1 kg m^2/s^2 = (1/2)(mass)[(0.5 kg m/s^2)/mass]^2

solving for mass, you obtain:

mass = 0.125 kg ]ans.

Daniel Kurniawan
Dec 31, 2013

Kinetic Energy = 0.5 * Mass * Velocity^2

Momentum = Mass * Velocity

Kinetic Energy = 0.5 * Momentum * Velocity

v = Kinetic Energy * 2 / Momentum

 = 1 * 2 / 0.5

 = 4

Momentum = Mass * Velocity

Mass = Momentum / Velocity

 = 0.5 / 4

 = 0.125

thanks mate

Harshit Sharma - 7 years, 3 months ago

Let p p = momentum, K E KE = kinetic energy, v v = velocity, and m m = mass.

Recall that K E = 1 2 m v 2 KE = \frac{1}{2}mv^{2} and p = m v p = mv .

We now have a system of equations:

1 J = 1 2 m v 2 1 J = \frac{1}{2}mv^{2} ( 1 ) (1)

0.5 k g × m / s = m v 0.5 kg \times m/s = mv ( 2 ) (2)

Substituting ( 2 ) (2) into ( 1 ) (1) , we get 1 4 v = 1 \frac{1}{4}v = 1 m / s m/s .

Therefore, v = 4 m / s v = 4 m/s ( 3 ) (3) .

Substituting ( 3 ) (3) into ( 2 ) (2) , we get m = 1 8 k g = 0.125 k g m = \frac{1}{8} kg = 0.125 kg .

Hence, the frog's mass is 0.125 k g \boxed{0.125 kg} .

Agus Faisal
Apr 27, 2014

p = mv |||||||||||| 1/2 = mv ||||||| v= 1/2m |||||||||||||||||||||||||||||||||||||| EK = 1/2 mv^2 |||||||||||||| 1 = 1/2 m (1/2m)^2 |||||||||||||||||||| 1 = 1/2 . m . 1/4m^2 |||||||||||||||||||||| 1 = 1/8 m |||||||||||||| 8m = 1 |||||||||||||||| m = 1/8 |||||||||| m = 0,125 kg

Aravind Raj
Mar 3, 2014

KE=P^2/2m 1=.25/2m m=0.125kg

we know that K.E=P P/2M......SO m=P P/2 K.E=.5 .5/1*2=.125

we know, K.E= p^2/2m given m is mass of body, p is momentum nd KE is kinetic energy of the body.. so changing the equation as m=p^2/2KE nd placing the values we get the result

chor

Abhijeet Singh - 7 years, 3 months ago
Agasthiyaraj L
Jan 22, 2014

E=p^2/(2m)

Ashwin Ramgopal
Dec 19, 2013

It is the direct application of the formula

KE = p^2/2m

Where p is momentum of body

1J = 0.5^2/2m

1J = 1/8m

=>m = 1/8 = 0.125 Kg

Wira Irawan
Dec 16, 2013

First , 1/2 m v^2 = 1 joule , arrange it and we found v^2=2/m Then, input the value of v into the momentum, then we got the answer 0.125

Fengyu Seah
Nov 2, 2013

Since kinetic energy = p 2 2 m = \frac{p^2}{2m} , 1 = 0. 5 2 2 m 1 = \frac{0.5^2}{2m} .

Therefore, 2 m = 0.25 2m = 0.25 and m = 0.125 m = 0.125 .

So, the mass of the frog is 0.125 0.125 kg.

Tejwinder Singh
Nov 2, 2013

KE = 1/2 mv.v
Here p ( momentum ) = 0.5 kg. m/s And KE (kinetic energy) = 1 joule (J )

Putting values of KE and p, we get

1 = 1/2 (0.5 ) v

2 = ( 0.5 ) v

V= 4

Also, p = mv

0.5 = m (4)

M = 0.125

Ojas Jain
Oct 31, 2013

MOMENTUM=mv-----------------------1, KINETIC ENERGY=1/2mv^2-----------------2, DIVIDING 1 AND 2,WE GET, MOMENTUM/KINETIC ENERGY=2/v

ACCORDING TO GIVEN CONDITION, 0.5=2/V V=2/0.5

KINETIC ENERGY=1/2mv^2 1 =1/2 m[4]^2 2/16 =m i.e 0.125 =m

so,you are living in mumbai

Devashish Dewalkar - 7 years, 7 months ago

0 pending reports

×

Problem Loading...

Note Loading...

Set Loading...