Question

@Abhisar Please help me solve this question...
The efficiency of a car engine is 25%.The total resistance to motion is 1000N when the car is moving at a constant velocity.If the energy in one litre of petrol is 40MJ,how far can the car travel with 1.0 litre of petrol?

Answer 1

Given energy in 1 litre petrol is 40Mj and the efficiency is 25% so the car will use 10Mj of energy

Answer 2

Total work done will be equal to 10Mj, Work=Force\(\times\)Distance

Answer 3

set up the equation and solve it for s

Answer 4

Why the car will use 10MJ of energy?

Answer 5

Because efficiency is 25%

Answer 6

I'm still don't understand...

Answer 7

25% of 40Mj=10Mj

Answer 8

The car is able to use only 25% of total fuel energy

Answer 9

O...got it...I go to try 1st...

Answer 10

ok

Answer 11

How can i get distance?

Answer 12

Force\(\times\)Distance=Work, Here work is 10Mj and Force=1000N

Answer 13

That 10MJ is work?

Answer 14

yes, Energy=Work

Answer 15

And what is M?

Answer 16

Mj=Mega joules

Answer 17

1 000 000 joules

Answer 18

Got it ?

Answer 19

1000000/1000 is 1000,but the book answer is 10km...

Answer 20

10Mj= 10\(\times\) 10\(^6\) = 10\(^7\) joules, now distance will be equal to 10Km

Answer 21

1Mj=10\(^6\) j

Answer 22

Ya...I forgot to time 10...OK...final answer is 10km...

Answer 23

If just give power,Force and speed,how can i calculate the efficiency?

Answer 24

I am not getting ur question !
Efficiency = Output/Input * 100

Answer 25

and g

Answer 26

this is the question...
The power of an electrical motor is 200W.It is used to raise a load of 100N at a constant speed 0.6m/s.What is the efficiency of the motor?(Take g=10m/s2)

Answer 27

Tell me the formula of power ?

Answer 28

Power=FV

Answer 29

Power = Work done/Time

Answer 30

now 200 W means that the motor consumes a energy of 200 joules per second but pulls only 100 N per second.

Answer 31

Efficiency= 100/200*100=50%

Answer 32

Book Answer is 30%

Answer 33

And why i cannot use P=FV?

Answer 34

Yes, you will have to use P=F.V

Answer 35

P=100*0.6=60W

Answer 36

Now, output power will be 60W and input power is given 200W

Answer 37

Efficiency will be 60/200*100=30%

Answer 38

Got it ?

Answer 39

Ok..I got it...But how can identify which is input power and output power?

Answer 40

The power which is used to perform work or is supplied is input.

Answer 41

OO...What is the difference between P=work done/time and P=F.S?

Answer 42

Both are same !
Just two diff ways to obtain same thing.

Answer 43

ok...got it...

Answer 44

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Answer 45

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Answer 46

What is resistive force?

Answer 47

Force which resist motion.

Answer 48

If the momentum is conserved,what formula i want to use?

Answer 49

Post it as new question !