Physics: Chapter Three (homework)
Show that the momentum for a 2-kg brick parachuting straight downward at a constant speed of 8m/s is 16kg*m/s
2kg x 8 m/s = 16kgm*s (downward)
How much momentum does an object at rest have?
An object at rest has no momentum
Why is it advantageous, in karate, to apply a force for a short time?
By using quick moves, the force is applied in a quick time which causes a greater impact force?
Railroad car A rolls at a certain speed and makes a perfectly elastic collision with car B of the same mass. After the collision, car A is observed to be at rest. How does the speed of car B compare with the initial speed of car A?
Car B is now going the initial speed of car A because they transferred momentum. Car A now has car B's initial momentum and car B now has car A's initial momentum.
Show that impulse on a baseball that is hit with 100 N of force in a time of 0.5 s is 50 N.s.
F= 100 N t= 0.5 s (100N)(0.5s)= 50N.s.
Show that 2.4 J of work is done when a force of 2.0 N moves a book 1.2 m (1 N * m = 1 J)
F= 2.0 N d= 1.2 m (2.0N)(1.2m) = 2.4J
What is the equation for kinetic energy?
Kinetic Energy = 1/2 mass x velocity^2 ; KE = 1/2m*v^2
Jeannie Beanie (mass 40 kg), standing on slippery ice, catches her leaping dog, Daisy (20 kg), who leapt into her arms after running across an adjacent field at 6 m/s. Use the conservation of momentum to show that she speed of Jeannie and her dog after the catch is 2 m/s.
Momentum (of Daisy) = Momentum (of Jeannie + Daisy) Daisy: 20kg, 6m/s. Jeannie: 40kg. Jeannie + Daisy: 60kg Daisy Momentum: (20kg)(6m/s) =120kg*m/s 120kg*m/s=(60kg)v 120kg*m/s/60kg = v v= 2m/s
Two cars are raised to the same elevation on service station lifts. If one car is twice as massive as the other, how do their potential energies compare?
The car that is twice as massive has twice as much potential energy as the other car.
Which has greater momentum: an automobile at rest or a moving skateboard?
The skateboard has greater momentum
What is the equation for work?
Work= Force x Distance (J= Fd)
What is the equation for gravitational potential energy?
gravitational potential energy = mass (m) x acceleration due to gravity (g) x height (h) ; PE = mgh
What is the equation for impulse?
impulse = force x time (Ft)
Show that the kinetic energy of a 1.0 kg book tossed across the room at a speed of 3.0 m/s is 4.5 J (1 J is equivalent to 1kg(m/s)^2)
m= 1.0 kg v= 3.0 m/s 1/2(1.0kg)*(3.0m/s)^2= 4.5kg(m/s)^2 -> 4.5 J
Show that when a 3.0 kg book is lifted 2.0 m, it's increase in gravitational potential energy is 60 J
m= 3.0 kg g= 10m/s^2 h=2.0m (3.0kg)(10m/s^2)(2.0m)= 60 J
What is the equation for momentum?
momentum = mass x velocity (mv)
