When a bomb is initially at rest and then explodes, the total momentum of the de

Question

When a bomb is initially at rest and then explodes, the total momentum of the debris is zero. But the kinetic energy goes from zero to some non-zero amount. Where is the energy coming from? Would your friend be correct saying that energy is not conserved in this situation? (b) What is a reversible interaction? Give an example and explain why it is considered reversible. (c) A 625 gram basketball is dropped from a height of 1 meter. After its speed just after hitting the ground is only 85% of the speed it has when it hits the ground (c1) What is its kinetic energy before and after hitting the ground (c2) What height does it reach assuming it bounces back up vertically? (c3) What types of energy increase between the ball and the ground while the ball is in the process of colliding with the ground? A 625 gram basketball and a 3 gram ping-pong ball are dropped with the ping-pong ball only a tiny distance directly above the basketball. They are dropped from a height of 1 m (of course, the ping-pong ball is a bit higher than that, but it will collide with the top of the basketball after dropping about 1 meter too). The basketball bounces first, losing 15% of its ground-impact speed due to the inelastic effects. Almost instantly after bouncing, the basketball collides with the ball. Use potential energy to compute the speeds of the ping pong and basketball just after the basketball bounces off the ground but just before they collide. Use momentum conservation and energy conservation to work out the kinetic energy of the ping-pong ball just after it collides elastically with the basketball. What is the ping pong ball's vertical displacement after it rises to its maximum height?

Explanation / Answer

a) according to the law of energy conservation the energy cannot be destroyed or created and it can only be converted. In case of bomb at first it is at rest which means the total momentum=0.But we get some amount of kinetic energy. This energy comes from the internal reactions of the bomb or the kinetic energy is the conversion of the chemical energy. Therefore , energy conveservation theory is still true as we get other two components of energy as EM and sound components after the exploson.

b) In any reversible process we can get back the initial particles if the process is reversed. In the similar way we can get back the initial reactants from the products if the reversible interactions are reversed. As an example electron-neutrino conversion is an reversible process. The electron can emit a W- and converted into neutrino. In a similar way if the neutrino absorves W- it can return the initial electron. Therefore, it is an reversible interaction.

c1) after hitting the ground the speed become 85% of the initial speed v

then before hitting ground the K.E.=1/2..625v^2

after hitting the ground K.E.=1/2.625.(85v/100)^2

now using 1/2mv^2=mgh we get v=sqrt(2gh)=sqrt(2*9.8*1)=4.427m/s

then before hitting ground the K.E.=1/2..625v^2=1/2*.625*(4.427)^2=6.124 J

after hitting the ground K.E.=1/2*.625.(85v/100)^2=1/2*.625*(85*4.427/100)^2=4.425J

c2) time taken to reach the ground is t=sqrt(2h/g)=sqrt(2*1/9.8)=.451sec

using H=ut-1/2gt^2 we get the bouncing height

so u=velocity after hitting the ground=3.76m/s ,t=.451sec

therefore H=3.76*.451-1/2*9.8*.451^2m=.699m

c3) In the process of coliding the interaction energy increases between ground and ball

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