physics question! need help please?

Arslan K

New member
A 5.10 kg block is sent sliding up a plane inclined at θ = 37.0° while a horizontal force F of magnitude 50.0 N acts on it. The coefficient of kinetic friction between block and plane is 0.310.
(a) What is the magnitude of block's acceleration?
(b) The block's initial speed is 4.10 m/s. How far up the plane does the block go?
 
<< What is the magnitude of block's acceleration? >>

I will ASSUME that the "horizontal force of magnitude 40 N" is directed parallel to the incline. Thus being said,

50 - F = ma

where

F = frictional force acting on the block
m = mass of the block
a = acceleration of the block

Since

F = µN = µ(mgcos 37), then the above equation becomes

50 - µ(mgcos 37) = ma

and substituting appropriate values,

50 - 0.310(5.10)(9.8)(cos 37) = 5.1(a)

and solving for "a"

a = 7.38 m/sec^2

<< The block's initial speed is 4.10 m/s. How far up the plane does the block go? >>

Use the law of conservation of energy,

KE @ bottom of incline - Friction loss = PE when block stops

KE @ bottom of incline = (1/2)(5.1)(4.10)^2 = 42.86 joules

Friction loss = 0.310(5.1)(9.8)(sin 37)(L)

PE when block stops = 5.1(9.8)(L*sin 37)

where

L = distance along incline travelled by block

The above equation then becomes,

42.86 - 0.310(5.1)(9.8)(sin 37)(L) = 5.1(9.8)(L*sin 37)

and solving for "L"

L = 1.09 m

Hope this helps.
 
Back
Top