Physics Question - very easy but dont know what formual to use - PLEASE HELP?

Question

here is the question -

A block of mass 15 kg stars from rest and slides a distance of 6 m down an inclined plane making an angle of 40 degrees with the horizontal. The coefficient of sliding friction between block and plane is 0.4.
The acceleration of gravity is 9.8 m/s^2.

a. What is the net force on the block along the incline? Answer in units of N.

b. What is the speed of the block after sliding 6 m? Answer in units of m/s.

c. What would be its speed if friction were negligible? Answer in units of m/s.

Your HELP is much APRRECIATED

THANK YOU

Answer 1

The best help I can offer is learn the physics, then the equations will be easier to remember.

Net force f acting on a mass m will acclerate a that mass. So f/m = a from knowing the physics. You know the mass, now figure out the net force by ID'ing all the forces and adding them up. And, this is important, the net force must act along the surface of the ramp to accelerate the block along the surface.

Two forces on the block are clear: weight W and friction F. What's the physics? Weight is the force of gravity pulling on a mass m. Thus, W/m = g where g is the acceleration of mass m due to the force of gravity, which we call weight.

But weight acts up and down, not along the surface of the ramp. So we need to find w = W sin(theta) = mg sin(theta), which is that bit of weight acting parallel to the ramp inclined at theta = 40 degrees.

Friction force F depends on the coefficient of friction k = .4 and something called the Normal weight (N). As Normal weight is just that portion of W that pushes perpendicular on the ramp, \we have N = W cos(theta) which specifies the normal/perpendicular portion of that weight. Thus, F = kN = k W cos(theta) = kmg cos(theta). And all that came from knowing the physics. Nothing memorized here.

Now we can do the net force f = ma = (w - F) = W sin(theta) - k W cos(theta) = mg(sin(theta) - k cos(theta)); so that a, the acceleration rate of the block sliding down the slope, = g(sin(theta) - k cos(theta))

One more physics lesson. Potential energy PE = mgh = mg S sin(theta) = 1/2 mv^2 + kFS = 1/2 mv^2 + kmgS cos(theta) = KE + FE, kinetic energy plus friction energy (FE = kFS) lost as heat (work) after sliding S distance; where S = 6 m, the distance of slide and h is the starting height of the block on the ramp as measured from the height after the block has slid S. In other words, the zero point height from which the potential energy PE is measured is the height the block is at after sliding S = 6 meters.

And now we have everything we need to answer the questions...by understanding the physics.

a. Net force f = w - F = ma = mg sin(theta) - k mg cos(theta) = mg(sin(theta) - k cos(theta)); where m = 15 kg, g = 9.81 m/sec^2,, k = .4, and theta = 40 degrees. You can do the math. [Note that a = g[sin(theta) - k cos(theta)], you'll see this relationship again.]

b. From mg S sin(theta) = 1/2 mv^2 + kFS = 1/2 mv^2 + kmgS cos(theta) we can write 1/2 mv^2 = mg S sin(theta) - kmgS cos(theta). Then v^2 = 2Sg[sin(theta) - k cos(theta)] and v = sqrt(2Sg[sin(theta) - k cos(theta)]) You can do the math.

c. Set k = 0 to the above to make it frictionless. Then v = sqrt(2Sg sin(theta)); you can do the math.

My point is this. If you are taking a physics class, learn the physics. The equations will take care of themselves. At the very least, the number you actually have to memorize will be minimized. At the most, you will have a clearer understanding of the physics and be able to derive some equations of your own....which is great fun.

Answer 2

you recognize what, as quickly as I study your question, i assumed that I understood the respond, yet interestingly I don. A damaging acceleration could advise that the object is slowing down ("deceleration" concept this is not a real notice, rather). till there is loads of air resistance, i don't comprehend why it may do this. additionally, I continually get tripped up as to which acceleration equation to apply... so, apologies for finding out to purchase your hopes up. consistent with danger the internet website under will help.