1. WHere is the work in holding a 50 poundweight over your head? If is resting o

Question

1. WHere is the work in holding a 50 poundweight over your head? If is resting on the floor, is the floor doing work? Why are you worn out?

2. A airplane is moving in a large circle at a fixed speed. Is kinetic enrgy conserved? Is momentum conserved? Suppose there is friction with the air (there is), but the speed is constant. Is kinetic energy of the plane conserved? Is total energy conserved?

3. A sled of mass m is pushed for 5 secondsat a constant force. A sled of mass M (more) is also pushed for 5 seconds. THe force is the same in each case. WHat is the momentum of each sled? How do they compare? What is the energy of each sled? How do they compare?

4. The same as question 3, except each sled is pushed for 5 meters instead of 5 seconds.

5. Two objects collide and rebound elastically. Write down the equations for momentum and kinetic energy conservation. Let these same two objects collide inelastically and fuse. Write the momentum equation. Attempt to write the equation for Kinetic Energy conservation. can this be simultanesously true with momentum conservation? If not, which conservation equation is correct, and what is wrong with the other?

Please show work and explain.

Explanation / Answer

1]in this step i m doing any work by the potential energy that is required in keeping the load at the head

so the work is holding over my head as potential energy

2]if the plane is moving with fixed speed

KE ----> remains conserved as KE is a scalar quantirty it doesnt depends on the direction of the velocity

Momentum ----> the direction of velocity is continously changing so the momentum changes direction continously but the magnitude remains the same

if there is friction and the speed remains conserved than also the KE is not conserved

but the tota;l energy isnot conserved as there is a external force on the system

3]the momentum of each sled = mass * velocity

momentum of m = mv

velocity after 5sec = v= u+ at

= Force = ma

= a = F/m

so V = 0 + 5* F/m

so momentum = 5F

and the same for M mass = 5F

they both are equal

the energy of both the ,mass have KE = 0.5 M v^2 and 0.5 mv^2

4]now the distance is same that is 5 metres

so the momentum needs to found by the KInematic equation

momentum = mv

v^2 = u^ + 2as

a = F/m

so we knpow u = 0

S = 5m

so we find the value of V and place it in the equation of momentum and compare the two momentums

5]

-e= V2-V1/U2-U1

e for elastic = 1

in the first case the momentum can also be conserved

and energy conservation can be applied

but in case of inelastic collision

momentum can be cpnserved before and after the ciollision

but the energy is not conserved

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