Question

A ruler stands vertically against a wall. It is given a tiny impulse at θ=0∘ such that it starts falling down under the influence of gravity. You can consider that the initial angular velocity is very small so that ω(θ=0∘)=0. The ruler has mass m= 100 g and length l= 35 cm. Use g=10 m/s2 for the gravitational acceleration, and the ruler has a uniform mass distribution. Note that there is no friction whatsoever in this problem. (See figure)

(a) What is the angular speed of the ruler ω when it is at an angle θ=30∘? (in radians/sec)

ω=

unanswered
(b) What is the force exerted by the wall on the ruler when it is at an angle θ=30∘? Express your answer as the x component Fx and the y component Fy (in Newton)

Fx=

unanswered
Fy=

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(c) At what angle θ0 will the falling ruler lose contact with the wall? (0≤θ0≤90∘; in degrees) [hint: the ruler loses contact with the wall when the force exerted by the wall on the ruler vanishes.]

θ0=

Answer 1

yes please.. that's the only question where I'm stuck too..

Answer 2

Me too!!!

Answer 3

Hi Teresa, can you do rocket problem me pls?

Answer 4

p: percentage (4.5% is burned in 155s)
m:mass of rocket
u:fuelspeed in meter/s!

v=u*ln(1/(1-p))=1500*ln(1/0.955)

a=v/t = 69.065/155= 0.4455

Answer 5

Hi Teresa, in my problem, question says The rocket burns 10 % of its mass in 290 s (assume the burn rate is constant).
What is the speed of the rocket after a burn time of 145.0 s?

How did you find 4.5% is burned in 155 sec? Pls.
Thank you very much

Answer 6

because they ask you for half of the time,
so in your case in 145 it gets burned 5% in 145 seconds

Answer 7

Thank you very much Teresa. I got green check. Now time for rular one..

Answer 8

in the equation above what is the "ln"?

Answer 9

"ln" is like log..it is in your calculator

Answer 10

is the "u" the ejected fuel in m/s instead of km/s?

Answer 11

hai Teresa can u help me for this Rocket question i don't know how to get 0.955 in the above ans !

Consider a rocket in space that ejects burned fuel at a speed of vex= 2.0 km/s with respect to the rocket. The rocket burns 11 % of its mass in 250 s (assume the burn rate is constant).

(a) What is the speed v of the rocket after a burn time of 125.0 s? (suppose that the rocket starts at rest; and enter your answer in m/s)

v=

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(b) What is the instantaneous acceleration a of the rocket at time 125.0 s after the start of the engines?(in m/s2)

a=