- #1

- 4

- 0

HW Template missing as it was moved from another forum

W=F.d cos Ɵ, in a problem Ɵ=30, but in the solution he used Ɵ=60, and vice versa in other problems, can anyone explain why?

Last edited by a moderator:

You are using an out of date browser. It may not display this or other websites correctly.

You should upgrade or use an alternative browser.

You should upgrade or use an alternative browser.

- Thread starter Sculter
- Start date

- #1

- 4

- 0

HW Template missing as it was moved from another forum

Last edited by a moderator:

- #2

Doc Al

Mentor

- 45,377

- 1,754

- #3

- 4

- 0

problem like:

*calculate the force acting on an object if the work done to move it a distance 50m equal 2500J and if the angle between the force and the perpendicular to motion is 30

the answer: w=fd cosθ , F=2500/50xcos60 = 100N

*a man of mass 70kg. goes upstaris of lenth 50m. calculate the work done if g=10m/s

-answer W=Fd cosθ, 70x10x50 x cos30

-problem with no changing in angles-

*a force of 100N acts on an object and moves it a distance 2.5m, calculate the work by the force if the force is inclined by an angle 60 on the direction of motion

answer: W=100x2.5x cos60= 125J

----------

i don't know why he changes angles and when, i think i'm missing something.

Last edited by a moderator:

- #4

Doc Al

Mentor

- 45,377

- 1,754

Note that the angle given is not between F and d, but between F and the*calculate the force acting on an object if the work done to move it a distance 50m equal 2500J and ifthe angle between the force and the perpendicular to motionis 30

the answer: w=fd cosθ , F=2500/50xcos60 = 100N

Again, the angle given is the angle of the stairs with the horizontal. What you need is the angle between the force (gravity) and the displacement.*a man of mass 70kg. goes upstaris of lenth 50m. calculate the work done if g=10m/s2

-answer W=Fd cosθ, 70x10x50 x cos30

Here they just give you the required angle, so you can just plug it in.-problem with no changing in angles-

*a force of 100N acts on an object and moves it a distance 2.5m, calculate the work by the force if the force is inclined by an angle 60 on the direction of motion

answer: W=100x2.5x cos60= 125J

To use the work formula you need the angle between the force and the displacement. Sometimes you'll be given that angle directly; other times you'll have to figure out the correct angle to use.i don't know why he changes angles and when, i think i'm missing something.

- #5

- 4

- 0

oh, great now i know why, i didn't realize it, thank you

but how do i find the angle?

but how do i find the angle?

- #6

Doc Al

Mentor

- 45,377

- 1,754

You are welcome.oh, great now i know why, i didn't realize it, thank you

Start by drawing yourself a diagram. And use the properties of right triangles. (For example, the two angles of a right triangle are complementary. They add to 90 degrees.)but how do i find the angle?

- #7

- 4

- 0

Thanky you very much!

Your really helped me

Your really helped me

Share:

- Replies
- 3

- Views
- 22K