Physics Help -- PLEEEASE!!

R.D

Ok, I'm really weak when it comes to Physics but have to do it in my course -- studying Applied Bioscience. Spent the last two hours on this one question which is supposed to be handed in tomorrow along with several others as part of my continous assessment. Anyhoo's here's the question...

An object of mass 200kg initially moving along a horizontal surface with a velocity of 15 ms-1 is brought to rest by a frictional force of 600 N.

Calculate (a) the deceleration
(b) the distance travelled
(c) coefficient of friction
(d) the work done in bringing it to rest.

If I could just calculate the deceleration I'm sure I could manage the rest, it's just I'm not sure how to go about finding the deceleration because of the lack of info in the question.

So far I think I've to take gravity into consideration and use the formula 'v= u + gt' to get the time, but then what -- do I use that 't' value to get the acceleration in the formula 'v = u + at', man I'm so confused. Any help would be very much appreciated!!

Spear

R.D wrote:

If I could just calculate the deceleration I'm sure I could manage the rest, it's just I'm not sure how to go about finding the deceleration because of the lack of info in the question.

It's just F=ma

Delphi91

R.D wrote:

An object of mass 200kg initially moving along a horizontal surface with a velocity of 15 ms-1 is brought to rest by a frictional force of 600 N.

Calculate (a) the deceleration
(b) the distance travelled
(c) coefficient of friction
(d) the work done in bringing it to rest.

(a) Use F=ma to find the deceleration.

(b) Once you have a, you can use v^2 = u^2 + 2as to get the distance travelled, where v is the final velocity (0 m/s) and u is the initial velocity (15m/s) [Remember to use a negative value for a]

(c) The coefficient of friction can be got from F=μR where F is the frictional force (600N) and R is the weight of the object (mg).

(d) The work done is the same as the loss in energy, which is the kinetic energy of the object. This is 1/2 mv^2 (where v = 15m/s)

Hope this helps.

Mike

Tar.Aldarion

I imagine it does, as it gives him all the answers. :P

It's all about formulae OP, the physics you are doing is fairly simple, so it'll all be about formulae that you are just given, log tables, Real World Physcs etc...

dudara

Delphi91 wrote:

(c) The coefficient of friction can be got from F=μR where F is the frictional force (600N) and R is the weight of the object (mg).

That's not quite right.

F = μN, where N is the normal reaction.

In the case of an object on a horizontal surface, then N equals the weight of the object. N will change if the object is on anything else other than a horizontal surface.

Tar.Aldarion

Well, isn't that what he said really?
I know he didn't mention the normal, but it is not relevent in this question.

Still, it's handy for the OP to know!

dudara

I know I was kind of nitpicking, but what he said, while giving you the right numerical answer, was not correct physics-wise.

Tar.Aldarion

Women

R.D

Thanks a million for the help last week guys, haven't been online since. I was able to work it out with all the info that was posted on here. Working on a new assignment due in Tuesday -- I'm happy enough with it except for the last question with looks impossible to work out. Anyhoo's thanks again!

Tar.Aldarion

What' s the last one?

R.D

Question ten has a drawing of a conveyor belt system, the info we're told is:

Rotational speed of motor = 120 RPM
Diameter of the drive pulley = 500mm
Diameter of idler pulley = 300mm

Then the questions are as follows --

(a) Calculate the speed of the conveyor belt in m/s

(b) What will be the speed of the conveyor belt if:

(i) the idler pulley is replaced with a 150mm diameter pulley.
(ii) the drive pulley is replaced with a 250mm diameter pulley.

---

After Christmas I'll have to look about getting grinds, can't get my head around it.

dudara

R.D wrote:

Question ten has a drawing of a conveyor belt system, the info we're told is:

Rotational speed of motor = 120 RPM
Diameter of the drive pulley = 500mm
Diameter of idler pulley = 300mm

Then the questions are as follows --

(a) Calculate the speed of the conveyor belt in m/s

(b) What will be the speed of the conveyor belt if:

(i) the idler pulley is replaced with a 150mm diameter pulley.
(ii) the drive pulley is replaced with a 250mm diameter pulley.

---

After Christmas I'll have to look about getting grinds, can't get my head around it.

For part (a) v = w*r (w is omega, the angular velocity) and r is the radius.

To work out the angular velcoity, take the rotational speed and convert it to revs per second. Then multiply by 2*PI.

Now you need to think about the relationship between the idler and driver pulleys.