1) What is the kinetic energy of a bowling ball with a mass of 6.5kg moving at a
constant speed of 15km/h?
2) A children's sled has a mass of 20kg and it moves on a horizontal ice rink
with an initial speed of 7 m/s. The coefficient of kinetic friction between the
sled and the ice rink is 0.2. Assuming all its kinetic energy is converted into
work done against friction, calculate the distance it travels until it comes to a
halt. Solve using the work-energy theorem, not kinematics equations.
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3) A heavy 50kg box of office supplies is standing on top of the BICSA Tower
at Avenida Balboa. This skyscraper is 267m high. If there is no air friction,
calculate the gravitational potential energy of the box relative to the ground
at:
(a) The top of the skyscraper.
(b) After it fell 150m.
4) I have a Jack-in-the-Box toy. It's a small music box with a crank on the side
that plays a tune while a clown puppet hides inside, waiting to pop out by
surprise. The puppet is attached to a spring that keeps it pressed down
inside the box and makes it jump out once the box opens. When the clown
is fully inside, the spring is compressed a total of 20 cm. If the constant of
the spring is equal to 30N/m, calculate the potential energy stored when the
clown is inside of the box.
5) Let's say that we put inside the office supplies box of problem #3 a big
printer with a mass 20kg. Will this difference in mass affect the final speed
that the box hits the ground with? Explain your reasoning using the work-
energy theorem.
No, because the only values that affect the final speed are gravity and height.
The mass only affects the energy.
6) Calculate the final speed that the box of problem #3 hits the ground
with,
using the work-energy theorem.
