Use Coupon: CART20 and get 20% off on all online Study Material

Total Price: R

There are no items in this cart.
Continue Shopping
Get instant 20% OFF on Online Material.
coupon code: MOB20 | View Course list

  • Complete Physics Course - Class 11
  • OFFERED PRICE: R 2,800
  • View Details
Get extra R 700 off

				   Q)The two blocks in an atwood machine have masses 2kg and 3 kg . find the work done by gravity during the fourth second after the system is released from rest?

Q)A block of mass 100 g is moved with a speed of 5 m/s at the highest point in a closed circular tube of radius 10 cm in a vertical plane. The cross- section of the tube is such that the block just fits in it. The block makes several oscillations inside the tube and finally stops at the lowest point. Find the work done by the tube on the block during the process.
Please give the answer by explaining the question and what should be our mindset at this questions. Thank you

7 years ago


Answers : (1)



          By solving these simple force equations,




          this'll give distance moved by the blocks in 4th sec.=1/2*(g/5)*(42-32)=7mtrs.  [this is a case of constant acceleration ;Snth=1/2a((tn)2-(tn-1)2]

Now 3kg. block moves down & 2kg. block moves up by the same 7 mtrs.So for 3kg. block  gravity do (+ve) work as force & displacement has same direction while for 2kg. block it is (-ve).Equivalently (3-2=1)kg. move down by 7mtrs. & so total work done by gravity=1*10*7=70 J(F.dr)

Here this much work done by the gravity is transferred to the system as increase in their total kinetic energy which you could find by applying(v=u+at & K.E.=1/2 mv2).What u've to keep in mind that in case of external conservative field present(gravity for the system here) you couldn't use total change in potential & kinetic energy(mechanical energy)=work done by external agency.To be safe you could always do the whole thing in most basic way as i've done the question here by using basic concepts & mathematical formula.But you should know the physics also!!!

Note:For more clarity & greater grasp on topic & physics in general consult "Resnick ,Hallidey & Walker "(i think chapter 7"Work & Energy" in 4th ed. ;i'm not sure though).

[Q.2]  Total change in mechanical enery of block=Total work done by frictional force(exerted by tube on the block)=(0.1*10*0.2)+(1/2*0.1*52)=1.45J.

Here frictional force being non-conservative force the above concept is used.Always keep in mind for any system

1. Only external force will do any work.That force being conservative change in total mechanical energy will be zero.(work done=change in pot. energy=change in kin. energy)

2.For non-conservative force work done=Total change in mechanical energy.

As for mindset for any problem(in all 3 subjects & especially in physics) never fudge the basics.Concepts must be understood fully & unambiguously & practiced regularly.

Good Luck!

7 years ago

Post Your Answer

Other Related Questions on Mechanics

A particle is moving with a uniform acceleration along a straight line. Its velocities at A and B are respectively 7m/s^2 and 17m/s^2. M is the mid point of A and B. If t1is the time tajen...
let total distance be x meter b/w A and B. them to mid – point the eqns. are: (x/2) = 7*t1 + 0.5at1^2..............(1) and v = 7 + a*t1 For M to B (x/2) = (a*t1 + 7)*t2 +...
2017 years ago
a ball is dropped on the ground from a height 10cm .if coifficient of restitution is 0.4, then find the height to which ball is rebound ?
Final velocity would be, v = root( 0 + 2g*10/100) = > root(2) m/s. From coeff. of restitution, v’ = ev = > 0.4*v Now let h be the height it rebounced then, 0^2 = (0.4v)^2 – 2gh h =...
Vikas TU 8 days ago
For aiims..should i prefer mechanical engineering book? By s chand(for physics)
S.Chand Physics book is fine for academics also even fine for preparation to some extent. prepare concepts clearly from it....
Santosh Datla 3 months ago
@ sakshi No, for aiims mechanical engg book is not required at all , i never practiced any mechanical or even any books from s chand , but still i am in. For aiims specially u require the...
Umakant biswal 3 months ago
a person with normal near point 25 cm using a compound microscope with objective of focal length 8 mm and an eye piece of focal length 2.5 cm can bring an object placed at 9 mm from the...
For sharp focus, image should be formed at infinity. For image to be at infinity, The image formed by the objective should be at the focus of the eyepiece. WKT, Magnification(m)= v o /u o...
Raveesh 2 months ago
Why there is not located 3 rd and 4 th sem chapters for preparation of jee main ?
You questons is not clear to us. Can you please reframe it. Thaks.
Vijay Mukati 6 months ago
have also give u many questions but i didnt got a single answer .
Dear student, We could not answer the question due to high traffic on our website. We will answer soon Thanks for having patience
Nishant Vora 6 months ago
View all Questions »

  • Complete Physics Course - Class 12
  • OFFERED PRICE: R 2,600
  • View Details
Get extra R 650 off

  • Complete Physics Course - Class 11
  • OFFERED PRICE: R 2,800
  • View Details

Get extra R 700 off

More Questions On Mechanics

Ask Experts

Have any Question? Ask Experts

Post Question

Answer ‘n’ Earn
Attractive Gift
To Win!!!
Click Here for details