# Work and energy

1. May 29, 2016

### alijan kk

1. The problem statement, all variables and given/known data
A body moves a distance of 10 meter along a straight line under the action of a force of 5 newtons. If work done is 25 joules, the angle which the force takes with the direction of motion of the body is:
a: 0 degree
b: 30 degree
c: 60 degree
d: 90 degree

2. Relevant equations
work=fdcostheta

3. The attempt at a solution
what formula should we use to get the degree or how to figure out it by making a picture?

2. May 29, 2016

### tommyxu3

Based on the work's definition, to be honest, the more precise version of what you wrote in the Relevant equations, you have to find $F\cdot d,$ since the force is a constant vector here. Hence by what you had, you can get $W=F\cdot d=|F||d|\cos\theta,$ which can lead you to what you want.

3. May 29, 2016

### alijan kk

work = FDcos
25=5*10*cose
25=50*cos
cos=25/50
cos=0.5

but what now? 1/2 or 0.5 is equalt to what?? help

4. May 29, 2016

### alijan kk

work = FDcos
25=5*10*cose
25=50*cos
cos=25/50
cos=0.5

but what now? 1/2 or 0.5 is equalt to what?? help

5. May 29, 2016

### tommyxu3

The value $0.5$ you get is the cosine of the angle $\theta,$ which the the angle of the force and the displacement. Do you realize these?

6. May 29, 2016

### Parsifal1

Inverse cos (0.5)=60

7. May 29, 2016

### alijan kk

yes but on calculator the value of cosetheta is 0.99?
can you get the answer of the given options above?

8. May 29, 2016

### tommyxu3

Now the question is given $\cos\theta=0.5$ and you have to find the $\theta$ between $0$ to $180$ degrees. Right?

9. May 29, 2016

### alijan kk

10. May 29, 2016

### alijan kk

yes it is 60 by using inverse cosine theta !

11. May 29, 2016

### Parsifal1

That's how you find x in cos(x)

12. May 29, 2016

### tommyxu3

You don't have to apply the idea of inverse function, though the same, but just have to know what you want, with some basic knowledge of trigonometry, like $\cos 60^{\circ}=\frac{1}{2}.$

13. May 29, 2016

### Parsifal1

25=(5*10)cos(x)
25/(5*10)=cos(x)=0.5
cos^-1 (0.5)=60

14. May 29, 2016

### alijan kk

oh! thank you for your quick help. appreciat

15. May 29, 2016

### alijan kk

yes you are right if have this value memorized i would have done thi question in seconds thankyou i will memorize cos30 cos60 and cos90 values right?

16. May 29, 2016

### alijan kk

thanks

17. May 29, 2016

### tommyxu3

If you keep learning other physics knowledge, then you'll keep being with these basic concepts, and finally you will memorize, or say acquire, them naturally.

18. May 29, 2016

### A@bhishek

60°

19. May 29, 2016

### alijan kk

yes you are right , this question is solved

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