# Work and energy

## Homework Statement

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

work=fdcostheta

## The Attempt at a Solution

what formula should we use to get the degree or how to figure out it by making a picture?

## Answers and Replies

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.

• alijan kk
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.

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

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

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?

• alijan kk
Inverse cos (0.5)=60

• alijan kk
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?

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

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

• alijan kk
Inverse cos (0.5)=60[/QUOTEo
OH! yes the inverse of 0.5 is 60 !!
but why we are using inverse cosine?

Now the question is given ##\cos\theta=0.5## and you have to find the ##\theta## between ##0## to ##180## degrees. Right?
yes it is 60 by using inverse cosine theta !

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

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}.##

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

That's how you find x in cos(x)
oh! thank you for your quick help. appreciat

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}.##
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?

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

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.

• alijan kk

## Homework Statement

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

work=fdcostheta

## The Attempt at a Solution

what formula should we use to get the degree or how to figure out it by making a picture?
60°

60°
yes you are right , this question is solved