A classic puzzle...
She either kicked it at a wall <em>exactly</em><em /> 10 foot in front of her, where the ball rebounded off the wall.
Or, she kicked the ball straight up, vertically, at a <em>90 degree angle,</em> where due to the law of gravity, which states that anything that goes up must come down, when the soccer ball reaches exactly 10 feet, it falls back down.
(Note: This is nearly impossible to achieve -- exactly 10 feet.)
If a person want to move a <span>heavy box across the room, he must apply a force that is greater than starting frictional force acted on the heavy box in order to get the box in motion. the frictional force is equal to coefficient of friction times the normal force, and normal force is approximately the weight of the object. so the force that must be applied must be greater than the wieght of the object.</span>
Answer:
h = 18.41 m
Explanation:
Given that,
Mass of a test rocket, m = 11 kg
Its fuel gives it a kinetic energy of 1985 J by the time the rocket engine burns all of the fuel.
According to the law of conservation of energy,
PE = KE = mgh
h is height will the rocket rise
So, the rocket will rise to a height of 18.41 m.
I will name block a as Ma=5 kg, block b as Mb=10 kg and mass of the pulley M=3 kg and radius as R. Since the system will accelerate in the direction of the block b because it has greater mass, I will take that direction as positive. Both blocks and the pulley have the same acceleration because the slipping on the pulley is neglected. First, the equations of motion:
Mb*g-Tg=MbαR and
Ta-Ma*g=MaαR,
where Ta and Tb are the tensions of the cord, g=9.81 m/s^2 and α is the angular accereration. Also a=αR where a is the acceleration of the system.
Now the equation of rotational dynamics of a solid body:
(Tb-Ta)R=Iα=(1/2)*M*R^2*α, where (1/2)*M*R^2 is the moment of inertia of a disc.
When we input Tb=Mb*g - Mb*α*R and Ta=Ma*g + Ma*α*R from the first two equations into the third we get: (Mb*g - Mb*α*R - Ma*α*R - Ma*g)*R=(1/2)*M*R^2*α.
We solve for α and get: α=(Mb*g-Ma*g)/((1/2)*MR+Mb*R+Ma*R)=2.97 rad/s^2.
We know that a=α*R and we easily get a=0.4455 m/s^2
