Kinetic force/force/tilted plane question

[jamiebean]

Homework Statement

A box of mass m=24.7kg is pushed upward with an acceleration a=8.5ms-2 by a horizontal force F. The slope on which the box rests makes an angle α=50 degree. What should be the force F? Refer to the figure below. The unit of the answer is N.

Relevant Equations

f=ma
kinetic friction coefficient=tan(angle)
kinetic friction force= tan(angle)x mass x g(9.8)

kinetic friction coefficient=tan(angle)
kinetic friction force= tan(angle)x mass x g(9.8)
by these 2 equations, I calculated kinetic friction equation=39.236N

by f=ma,
f= 24.7kg x 8.5ms-2
=209.95N

so the force required should be 209.95+ 39.236N=249.1863?

Im not sure, are there any other forces too? like contact force?Im confused

 

[Gaussian97]

Yes, there are more forces, like you say the contact or normal force must be present always that two bodies are in contact, also for all bodies with mass inside a gravitational field there is an extra force, which one?

 

[Merlin3189]

Since they don't mention friction, there is no way you can calculate the friction. You must assume there is no friction.

The "angle of friction" that you refer to is not the angle of the slope.

For sliding friction, the angle of friction is constant.
It is the angle whose tan is equal to the coefficient of friction.
I don't find it a very helpful concept.

 

[jamiebean]

Since they don't mention friction, there is no way you can calculate the friction. You must assume there is no friction.

The "angle of friction" that you refer to is not the angle of the slope.
View attachment 258108
For sliding friction, the angle of friction is constant.
It is the angle whose tan is equal to the coefficient of friction.
I don't find it a very helpful concept.

is the answer 1406.42N?

the force acting on the block- weight(24.7kg x 9.8) -normal force(24.7x(9.8+8.5))=net force(24.7x8.5)
the force acting on the block=904.01N

the force required=904.02/cos50
=1406.42N

??

 

[haruspex]

the force acting on the block- weight(24.7kg x 9.8) -normal force(24.7x(9.8+8.5))=net force(24.7x8.5)

You can't go adding and subtracting forces like that. You must choose a direction and only add and subtract those components parallel to the chosen direction.
So, pick a direction, list the forces that have a component in that direction and find those components.

 

[jamiebean]

You can't go adding and subtracting forces like that. You must choose a direction and only add and subtract those components parallel to the chosen direction.
So, pick a direction, list the forces that have a component in that direction and find those components.

so my calculation is wrong?
but my force acting on the block is tilted, not the force required.so this is still wrong? my force acting on the box is the same direction as acceleration a

 

[haruspex]

so my calculation is wrong?
but my force acting on the block is tilted, not the force required.so this is still wrong? my force acting on the box is the same direction as acceleration a

As I posted, you must first choose a direction. In this problem, there is a force you do not know and are not required to find: the normal force. So it makes sense to pick a direction in which that force has no component.
What direction is that? What forces have components in that direction? What is the sum of those components, and what is its result?