# Engineering Physics(Work done and energy) Help!!!

1. Oct 2, 2015

### Benny T

Q2 AND Q5 are the questions I struck in at the minute. For Q 2 , I wonder i could simply use change of kinetic energy=Work done, does the catapult gain the same amount of energy as the Jet fighter?? For Q.5, i have no idea where to start, could someone at least give me some kind of direction??

Question 2:2. Jet fighter J-15 is launched from an aircraft carrier with the aid of its own engines and a catapult. J-15 is 6020 kg and the thrust of the engines is 23000N. At lift off, J-15 has a kinetic energy of 4.5x107 J and has moved 87m from the rest. What is the work done by the catapult?

Question 5:5. 1 A small particle (so the volume can be ignored) with mass m is having a circular motion with constant speed v and radius R. Determine it’s kinetic energy. 5. 2 A thin, solid, uniform disk of radius R and mass M is rotating constantly around the vertical symmetric axis as shown below. The constant speed at the rim is v. Calculate the kinetic energy of the disc. (Hint: A rotating disc is composed of particles as described in 5.1 with various R and v(R))

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2. Oct 2, 2015

### haruspex

The catapult and engine both do work on the aircraft. How much work is done by the engine? How much total work is done on the aircraft?

For Q5, how fast is the particle travelling?

3. Oct 2, 2015

### Benny T

Q.2 engine has done 23000x87 of work , total work has to be 4.5 x10^7 J as this is the lift off energy(NOT SURE)? so work done by catapult should be 4.5x10^7-23000x87=42999000

4. Oct 2, 2015

5. Oct 2, 2015

### haruspex

Looks right....
But too many significant figures compared with the given data.

6. Oct 2, 2015

### Benny T

The result is surprising as the catapult actually do much more work than the engine itself (almost 21 times more)!!