Homework Help: Frictional Force

1. Apr 8, 2007

raman911

Frictional Fore

m=0.2kg
h1=1.65m
h2=0m
v1=0m/s
v2=4.02m/s

http://img339.imageshack.us/img339/7201/11ei1.png [Broken]

Calculate the frictinal Force

Last edited by a moderator: May 2, 2017
2. Apr 8, 2007

dvyu

i might be able to help - but what does the 'h' stand for

3. Apr 8, 2007

Staff: Mentor

Well? What have you done so far?

Hint: There are two ways to go about this: (1) you can calculate the acceleration using kinematics and use that to find the net force, or (2) you can use energy methods.

4. Apr 8, 2007

raman911

Kinetic Energy1=0J
Kinetic Energy1=2.1J
Gravitational Potential Energy1 =2.3J
Gravitational Potential Energy2 =0J

5. Apr 8, 2007

raman911

how vcan i find acceleration i haven't time

6. Apr 8, 2007

dvyu

The net force is equal to mass*acceleration

7. Apr 8, 2007

raman911

i know but how can i find net force and acceleration

8. Apr 8, 2007

dvyu

you need to use perpendicular and parallel components

9. Apr 8, 2007

raman911

Kinetic Energy1=0J
Kinetic Energy1=2.1J
Gravitational Potential Energy1 =2.3J
Gravitational Potential Energy2 =0J

10. Apr 8, 2007

dvyu

I havent done energy yet at school - I would have to use kinematics, sorry

11. Apr 8, 2007

raman911

$$Given$$
$$m=0.2kg$$
$$\Delta d=0m$$
$${v}_{1}=0m/s$$
$${v}_{2}=3.96m/s$$
$${h}_{1}=1.65m$$
$${h}_{2}=0m$$

$$Required$$

$${F}_{f}$$

$$Solution$$

$$v_{ave} = (v_1 + v_2)/2$$
$$v_{ave} = (0m/s + 4.02m/s)/2$$
$$v_{ave} = 2.01m/s$$

$$\Delta t = \Delta \vec d/\Delta v_{ave}$$
$$\Delta t = 2.52m/2.01m/s$$
$$\Delta t = 1.25s$$

$$\vec a = \Delta v / \Delta t$$
$$\vec a = (2.01m/s) / 1.25s$$
$$\vec a = 1.608m/s^2$$

$${E}_{T}={m}g\Delta h$$
$$={0.2kg}*9.8N/kg*1.65m$$
$${E}_{g}=3.234J$$

$${E}_{k}=(1/2)m{v}_{ave}^2$$
$$=(1/2)0.2Kg(2.01m/s)^2$$
$${E}_{k}=0.40J$$

$${E}_{T}={E}_{k}+{W}_{f}$$
$$3.234J=0.40J+\vec F_{f}\Delta d$$
$$3.234J=0.40J+\vec F_{f}2.52m$$
$$\vec F_{f}=2.834J/2.52m$$
$$\vec F_{f}=1.112N$$

Last edited: Apr 8, 2007
12. Apr 8, 2007

raman911

nexxxt?????????/

13. Apr 8, 2007

Staff: Mentor

You don't need time--you have distance and speed.

14. Apr 8, 2007

raman911

i have height

i have n't distance

15. Apr 8, 2007

Staff: Mentor

Hint: If there were no friction, the mechanical energy would be constant. The loss of mechanical energy equals the work done by friction. (I did not check your calculations, but don't round off until the last step. Two digits is not accurate enough.)

16. Apr 8, 2007

raman911

syou mean distace is 1.65m

17. Apr 8, 2007

Staff: Mentor

Do you have the angle made by the ramp? (I can't read the writing on the diagram.)

18. Apr 8, 2007

raman911

i have not angle
only that

m=0.2kg
h1=1.65m
h2=0m
v1=0m/s
v2=4.02m/s

http://img339.imageshack.us/img339/7201/11ei1.png [Broken]

Calculate the frictinal Force

Last edited by a moderator: May 2, 2017
19. Apr 8, 2007

Staff: Mentor

If you don't have the distance over which the friction acts (or enough info to figure it out) I don't see how you can determine the friction force. (Sorry for not catching that earlier.)

After all, if the ramp were 100 m long you'd need much less friction than if it were 1 m long.

20. Apr 8, 2007

raman911

d=2.52m.........