Physics book slides off a horizontal

In summary: NERD ALERT squared!)In summary, a physics book slides off a horizontal table top with an initial velocity of 1.60m/s and strikes the floor after 0.440s. Using the formula x(t) = x(0) + v(0)t + 1/2at^2, the height of the table top above the floor is found to be 0.949m. The book also has a vertical component of velocity just before reaching the floor, which can be found using the formula v = at, with a value of -4.321m/s. The book will land either face up or face down depending on its horizontal launch velocity and the orientation of its edge.
  • #1
COCoNuT
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A physics book slides off a horizontal table top with a speed of 1.60m/s . It strikes the floor after a time of 0.440s . Ignore air resistance.

the following are given:
v(0)=1.60
t= 0.440s

ok this is the question

Find the height of the table top above the floor. Take free fall acceleration to be g=9.80m/s^2 .

i need to use this formula:
x(t) = x(0) + v(0)t + 1/2at^2 <-- height formula

the thing is why is v(0)t equal to zero? isn't the v(0) given in the problem? i know the correct answer and i know how the book done it, but they don't explain why v(0)t is equal to zero.

x(0) = 0 + 1/2(-9.8m/s^2)(.440s)^2 <--- i don't get why v(0) is zero
 
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  • #2
ok for that question the answer is 0.949m, so you don't have to do the calculations.

im working on this question:

Find the vertical component of the book's velocity just before the book reaches the floor. express in m/s

wouldnt it just be distance/time? 0.949m/0.440 = 2.15 which is incorrect
 
  • #3
the thing is why is v(0)t equal to zero? isn't the v(0) given in the problem? i know the correct answer and i know how the book done it, but they don't explain why v(0)t is equal to zero.

Your book should have explained that it was using the vertical component of the v(0) vector which happens to be zero (can you think of why this is so? Hint: the table is flat).


Find the vertical component of the book's velocity just before the book reaches the floor. express in m/s

wouldnt it just be distance/time? 0.949m/0.440 = 2.15 which is incorrect

The quantity you came up with was the average velocity of the book through it's transit from the table to the ground. There is an acceleration due to gravity, and as you know, accelerations are changes in velocity, so you will need to use the relation v = at; where a will of course be 9.8 m /s^2
 
  • #4
Gza said:
Your book should have explained that it was using the vertical component of the v(0) vector which happens to be zero (can you think of why this is so? Hint: the table is flat).




The quantity you came up with was the average velocity of the book through it's transit from the table to the ground. There is an acceleration due to gravity, and as you know, accelerations are changes in velocity, so you will need to use the relation v = at; where a will of course be 9.8 m /s^2

the answer is -4.321, but why v=at?
do i need the formula... Vfy = V(0)y - gt
v = -(-9.8)(0.44) = 4.321 which is wrong, why is that?
 
  • #5
Bonus question:

Does the book land face up or face down? :-)
 
  • #6
the answer is -4.321, but why v=at?
do i need the formula... Vfy = V(0)y - gt
v = -(-9.8)(0.44) = 4.321 which is wrong, why is that?

I apologize for my lack of explanation. I got v=at from the kinematical relation:

[tex]v_f = v_i + a\Delta t[/tex]

vi is simply zero since book slides off horizontally (with no initial vertical velocity.) [tex] \Delta t [/tex] is simply the time of flight.


You got the wrong answer because you added in another minus sign that didn't need to be there. Hope I helped! :smile:
 
  • #7
Does the book land face up or face down? :-)

You know, that would actually make an interesting problem to figure out! (NERD ALERT!) Correct me if I'm wrong but wouldn't it depend on the velocity of the horizontal launch? Launching the book at a critical speed would ensure it staying upright upon landing. Any other speed and it will either flip over or land on its edge.
 
  • #8
Gza said:
You know, that would actually make an interesting problem to figure out! (NERD ALERT!) Correct me if I'm wrong but wouldn't it depend on the velocity of the horizontal launch? Launching the book at a critical speed would ensure it staying upright upon landing. Any other speed and it will either flip over or land on its edge.

Yes, it would depend on the velocity at launch as well as whether the book edge is parallel to the edge of the table! This was inspired by my observation that if I ever knock my toast off the counter it seems always to land jelly side down!
 

What causes a physics book to slide off a horizontal surface?

A physics book will slide off a horizontal surface due to the force of gravity acting on it, as well as any other external forces such as friction or air resistance.

Why does a book slide off a horizontal surface faster when it is tilted?

When a book is tilted, the force of gravity acting on it has a component that is parallel to the surface, causing the book to accelerate faster down the slope.

How does the weight of the book affect its sliding motion?

The weight of the book affects its sliding motion by increasing the force of gravity acting on it, making it more likely to slide off the surface.

Can the speed of the book sliding off a horizontal surface be calculated?

Yes, the speed of the book can be calculated using the equation v = √(2gh), where v is the speed, g is the acceleration due to gravity, and h is the height of the slope.

What can be done to prevent a book from sliding off a horizontal surface?

To prevent a book from sliding off a horizontal surface, friction can be increased by adding a rough surface or placing a heavier object on top of the book to increase the normal force. Alternatively, the surface can be tilted at a smaller angle to reduce the downhill component of the force of gravity.

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