A block moving up a frictionless incline

AI Thread Summary
The discussion focuses on a physics problem involving a block projected up a frictionless incline. The initial kinetic energy of the block is calculated using the formula KE = 1/2 mv², resulting in 384 joules. This energy is then converted into potential energy (PE = mgh) to find the height at point B, calculated to be approximately 3.26 meters. For the total work done by gravity during the round trip, it is noted that since the net displacement is zero, the total work done is also zero. The conversation emphasizes understanding energy conversion to solve the problem effectively.
physicx_1
Messages
14
Reaction score
0

Homework Statement



A block of mass 12 kg is projected up a frictionless incline with an initial velocity of 8m/s. It just reaches a point B and then slides down again.

A) what is the potential energy of the block at B if its potential energy at A is taken as zero?

b) what is the vertical height h of B above A?

c)what is the total amount of work done on the block by the force of gravity during the round trip from A to B and back again to A?



Homework Equations





The Attempt at a Solution


I 've thought of a few ideas:

its equal to the initial velocity
converted into enery
cant remember the formula that makes velocity into kinetic energy
but EK = EP

but I don't really know how to do this question at all.

I think its about the equations of motion?

thanks for any help
 
Physics news on Phys.org
Don't jumble up your ideas...

First see the problem from the energy point of view: When you project a particle with a given velocity up an frictionless inclined plane, you provide some kinetic energy to it (=1/2mv2). This K.E will be continuously converted into potential energy (=mgh) as the body moves upwards, and at some point it will stop when whole of its K.E has been converted to P.E. So you can definitely determine the height to which it will move and answer the following questions thereafter.

Hope you understood how to get through the question!
 
Mandeep Deka said:
Don't jumble up your ideas...

First see the problem from the energy point of view: When you project a particle with a given velocity up an frictionless inclined plane, you provide some kinetic energy to it (=1/2mv2). This K.E will be continuously converted into potential energy (=mgh) as the body moves upwards, and at some point it will stop when whole of its K.E has been converted to P.E. So you can definitely determine the height to which it will move and answer the following questions thereafter.

Hope you understood how to get through the question!

thanks for your reply!

ok, so according to your response,

using (=1/2mv2), I get, 0.5 x 12 x 6sq. = 384 joules

is that how the first question is meant to be worked out?

if so, then you substitute 384 into mgh? and that's how you get the 2nd question?

I did that and using MGH for question 2 I have: 384joules = mgh. m=12 g=9.81 h=the unknown

so 384/12/9.81=3.26.

is that how its supposed to be?
 
can anyone help and do this 3rd question?
 
physicx_1 said:
can anyone help and do this 3rd question?
In part c, the particle returns back to A. So the net displacement is zero. Hence the work done should be...?
 
Kindly see the attached pdf. My attempt to solve it, is in it. I'm wondering if my solution is right. My idea is this: At any point of time, the ball may be assumed to be at an incline which is at an angle of θ(kindly see both the pics in the pdf file). The value of θ will continuously change and so will the value of friction. I'm not able to figure out, why my solution is wrong, if it is wrong .
TL;DR Summary: I came across this question from a Sri Lankan A-level textbook. Question - An ice cube with a length of 10 cm is immersed in water at 0 °C. An observer observes the ice cube from the water, and it seems to be 7.75 cm long. If the refractive index of water is 4/3, find the height of the ice cube immersed in the water. I could not understand how the apparent height of the ice cube in the water depends on the height of the ice cube immersed in the water. Does anyone have an...
Back
Top