Gayle runs at a speed of 4.00 m/s and dives on a sled, initially at rest on top of a frictionless snow-covered hill. After she has descended a vertical distance of 5.00 m, her brother, who is initially at rest, hops on her back and together they continue down the hill. What is their speed at the bottom of the hill if the total vertical drop is 15.0 m? Gayle's mass is 50.0 kg, the sled has a mass of 5.00 kg, and her brother's mass is 30.0 kg.
2007-10-22 07:36:35 · 2 answers · asked by Captain Whiskerboy Litterbox 3 in Science & Mathematics ➔ Physics
Gayle has an inelastic 'collision' with the sled.
Momentum is conserved during the collision
Momentum before = momentum after.
m1*V1 = (m1+m2)*V2
Gayle and the sled continue down, starting with initial velocity of V2. Because of that initial velocity, Gayle and the sled start sliding with an initial Kinetic Energy, call it KEi.
KEi = (1/2)*(m1+m2)*V2^2
They also have potential energy,
Ui = (m1+m2)*g*h
due to their 5 m vertical height over the point of the collision with the brother, so 5m worth of potential energy will be converted to more kinetic energy. Call the total when coming to the brother KE5.
Energy is conserved in the trip down to the brother.
Energy at the top = Energy when arriving at the brother (5 m vertically).
KEi + Ui = KE5 = (1/2)*(m1+m2)*V5^2
find V5 (the velocity when reaching the brother).
Momentum is also conserved during the next 'collision', when the brother jumps on.
Momentum before = momentum after.
(m1+m2)*V5 = (m1+m2+m3)*V53
find V53. OK the variable names are getting complicated but V53 is what I'm calling the velocity 5 m down, with all 3 masses combined.
Now repeat the conservation of energy work above (my paragraphs 2-4). Now you have all 3 masses combined and there is potential energy from 10 m elevation over the bottom of the hill.
2007-10-22 09:37:07 · answer #1 · answered by sojsail 7 · 0⤊ 0⤋
["Now repeat the conservation of energy work above (my paragraphs 2-4). Now you have all 3 masses combined and there is potential energy from 10 m elevation over the bottom of the hill."]
I dont understand that part that I have stated above!!
2014-06-13 07:13:46 · answer #2 · answered by tania 1 · 0⤊ 0⤋