# Mechanical Engineering - Engineering Mechanics - Discussion

### Discussion :: Engineering Mechanics - Section 1 (Q.No.5)

5.

The coefficient of restitution for elastic bodies is one.

 [A]. Correct [B]. Incorrect

Explanation:

Coefficient of restitution for elastic bodies is 0 - 1.

Coefficient of restitution for perfect elastic bodies is 1.

 Keshav said: (Dec 2, 2012) COR=1 for elastic collision not elastic bodies.

 Venugopal said: (Feb 2, 2013) What is mean by elastic collision?

 Sagar said: (Feb 8, 2013) When 2 bodies hit without losing momentum its elastic collision.

 Kumarsrinu said: (Feb 8, 2013) Hello @Venu, elastic means "two bodies are tends to elastic collision its coefficient of restitution e=1.

 Harish said: (Feb 16, 2013) The coefficient of restitution (COR) of two colliding objects is a fractional value representing the ratio of speeds after and before an impact, taken along the line of the impact.

 Nirav said: (Feb 28, 2013) What is coefficient of restitution?

 Shubhadip said: (Mar 29, 2013) Can anyone explain clearly regarding the difference of elastic bodies and elastic collision. I think then it will be clear to differentiate between the coefficients.

 Alok Kumar Choudhary said: (Apr 15, 2013) The difference between elastic & perfectly elastic body is if the body is perfectly elastic then the value of e is 1.

 Nikhil said: (Apr 19, 2013) Coefficient of restitution is a thing which will be experienced only when the bodies collide with each other and for a perfect elastic collision we need elastic bodies. Therefore this answer is wrong and e=1 for elastic bodies.

 Vignsh said: (Apr 25, 2013) What is elastic body?

 Sky said: (Apr 30, 2013) A body which can regain its original shape and size after removing the load (if load cause deformation in body) is called elastic body.

 Parvez said: (May 1, 2013) A bouncing basketball captured with a stroboscopic flash at 25 images per second. Ignoring air resistance, the square root of the ratio of the height of one bounce to that of the preceding bounce gives the coefficient of restitution for the ball/surface impact. The coefficient of restitution (COR) of two colliding objects is a fractional value representing the ratio of speeds after and before an impact, taken along the line of the impact. Pairs of objects with COR = 1 collide elastically, while objects with COR < 1 collide inelastically. For a COR = 0, the objects effectively "stop" at the collision, not bouncing at all. An object (singular) is often described as having a coefficient of restitution as if it were an intrinsic property without reference to a second object, in this case the definition is assumed to be with respect to collisions with a perfectly rigid and elastic object. COR = (relative speed after collision) / (relative speed before collision). The mathematics was developed by Sir Isaac Newton in 1687.

 Ritu Raj said: (May 1, 2013) The coefficient of restitution for elastic bodies is ZERO.

 Yo Yo Honey Singh said: (Jun 23, 2013) What is coefficient of restitution?

 Zeeshan said: (Jul 3, 2013) Coefficient of Restitution. Plastic Collision = 0. Elastic Collision = Between 0-1. Perfectly Elastic Collision = 1.

 Gaurav Sushant said: (Jul 19, 2013) There is difference in word perfectly elastic and elastic, e=1 perfectly elastic collision not for elastic collision.

 Prasad said: (Aug 5, 2013) COR is 1 for completely elastic collision, and elastic collision means collision between elastic bodies only. COR ranges from 0-1 for elastic bodies/collision. COR is 0 for plastic bodies/collision. Here he has mentioned elastic bodies only. Had he mentioned completely elastic, then it would be COR=1. So here COR is not equal to 1. Hence the option is also correct.

 Sharan said: (Aug 6, 2013) What is mean by coefficient of restitution?

 Guman said: (Aug 6, 2013) COR is the ratio of relative velocity after impact to the relative velocity before impact.

 Abhishek said: (Sep 8, 2013) Coefficient of restitution for: Perfectly plastic bodies 0. Plastic body is b/w 0-1. Elastic bodies b/w 0-1. Perfectly elastic bodies 1.

 Pinkesh said: (Sep 27, 2013) Please tell anyone clearly about Coefficient of restitution.

 Rathi said: (Nov 8, 2013) Coefficient of restitution for elastic bodies is 0 - 1. Coefficient of restitution for perfect elastic bodies is 1. So answer is B.

 Diwakar said: (Nov 19, 2013) Guys how can an elastic collision occur unless and until the bodies are elastic.?

 Jitendra said: (Jan 8, 2014) For perfectly elastic cor : 1. For perfectly inelastic cor : 0. For partially elastic cor: 0

 Abbas Sajid said: (Jan 10, 2014) The coefficient of restitution (COR) of two colliding objects is a positive real number between 0.0 and 1.0 representing the ratio of speeds after and before an impact, taken along the line of the impact. Pairs of objects with COR = 1 collide elastically, while objects with COR < 1 collide inelastically. For a COR = 0, the objects effectively "stop" at the collision, not bouncing at all. An object (singular) is often described as having a coefficient of restitution as if it were an intrinsic property without reference to a second object, in this case the definition is assumed to be with respect to collisions with a perfectly rigid and elastic object. The Coefficient of Restitution is equal to the Relative Speed After Collision divided by the Relative Speed Before Collision.

 Inderjeet Singh said: (Jun 9, 2014) Dropping several objects and measuring how high they bounce to determine the coefficient of restitution for each object. And because elastic body is zero because perfectly elastic.

 Srinivas said: (Jul 13, 2014) What is meant by COR?

 Chinmay Kuanar said: (Jul 26, 2014) COR Means Coefficient of Restitution.

 Umesh said: (Jul 28, 2014) What is mean by restitution?

 Asish Dutta said: (Nov 9, 2014) How to differentiate elastic body and elastic collision?

 Khurshid Alam said: (Dec 8, 2014) What is the difference between elastic and inelastic body/collision?

 Ahmed Nazir said: (Mar 17, 2015) Coefficient of Restitution is represented by 'e'.

 Ajithkumar said: (Jul 5, 2015) An elastic collision is defined as one in which both conservation of momentum and conservation of kinetic energy are observed.

 Akanksha said: (Jul 6, 2015) What is coefficient of restitution? Can you give examples of elastic collision b/w elastic bodies?

 Anil @ said: (Nov 20, 2015) Friends, how to find out the co-efficient of restitution. By using velocity and height of the object after impact.

 Arnab said: (Apr 11, 2016) The coefficient of restitution = Relative speed after collision/Relative speed before the collision. The coefficient of restitution for perfectly elastic bodies is 1 and for perfectly inelastic is 0. And it varies for 0 to 1. So, the correct answer would be [A].

 Ravi said: (May 10, 2016) Question is asked for elastic bodies hence, it's an elastic collision that is no K. E is lost. Therefore, the Coeff is 1.

 Amit said: (Jun 7, 2016) There is no perfect elastic body. An object that gains it's original shape after removal of the load is known as an elastic body. So according to my point of view answer is 1.

 Satish said: (Jul 26, 2016) What is collision?

 Ramkumar said: (Aug 2, 2016) Collision means change in size of body.

 Sandip Thakkar said: (Aug 24, 2016) For Perfectly Elastic - 1. For Elastic - 0 to 1. For Inelastic - 0.

 Ajay said: (Aug 31, 2016) Impact Collision of elastic bodies. If perfectly plastic body then its collision of restitution is e = 0. Because of plasticity the body won't regain to its original shape it will continue with its deformation. So, e = (v2 * -v1 *)/(v2 - v1). Due to plasticity the body wont go under elasticity, eg clay, if u through 2 clay to hit opposite and each other it wont have any (V2 * -V1 *) so it zero. e = 0/(v2 - v1) => e = 0. If perfectly elastic then (v2 * -v1*) = (v2 - v1). Therefor e = (v2 * -v1*)/(v2 - v1), = (v2 - v1)/(v2 - v1), = 1.

 Selva said: (Sep 13, 2017) What is mean by momentum.

 S.Junaid said: (Nov 3, 2017) Elastic body means it regain its original shape & size. But in actual practice it doesn't regain its dimensions 100%. If it regain its dimensions perfectly (100%) then it said to be perfect elastic body & its coefficient of restitution is one. The plastic body has zero coefficient of restitution because it doesn't regain its shape & size. And normal elastic body regain dimensions but not perfectly hence it's coefficient of restitution is variable but less than one.

 Abhilash said: (Dec 9, 2017) e = 0 for inelastic. e=1 for elastic.

 M Paulraj said: (Jan 24, 2018) The coefficient is 1 for an elastic collision, less than 1 for an inelastic collision, zero for a completely inelastic collision, and greater than 1 for a superelastic collision.

 Srimanta said: (Mar 21, 2018) It is the ratio of final to initiate relative velocity between two bodies after they collide. For perfectly elastic body COR is 1.

 Ajeesh said: (Nov 21, 2018) The coefficient of restitution is the ratio of the final to initial relative velocity between two objects after they collide. It normally ranges from 0 to 1 where 1 would be a perfectly elastic collision. A perfectly inelastic collision has a coefficient of 0, but a 0 value does not have to be perfectly inelastic.

 Anomie said: (Jun 11, 2019) "Perfectly" elastic body e=1.

 Birendra Kumar Verma said: (Aug 17, 2020) COR for perfectly elastic bodies will 1 only, hence answer of this question will be A not B.