Download Ch 5 Review Worksheet

Physics Review – Ch 5
Pg 193
Name ______________________________
2) Discuss whether any work is being done by each of the following agents and, if so, whether the work is
positive or negative.
a) a chicken scratching the ground
b) a person studying
c) a crane lifting a bucket of concrete
d) the force of gravity on the bucket in (c)
3) Furniture movers wish to load a truck using a ramp from the ground to the rear of the truck. One of the
movers claims that less work would be required id the ramp’s length were increased, reducing its angle
with the horizontal. Is this claim valid? Explain.
7) A person lifts a 4.5 kg cement block a vertical distance 1.2 m and then carries the block horizontally a
distance of 7.3 m. Determine the work done by the person and by the force of gravity in this process.
8) A flight attendant pulls her 70.0N flight bag a distance of 253m along a level airport floor at a constant
speed. The force she exerts is 40.0N at an angle of 52.0º above the horizontal. Find the following:
a) the work she does on the flight bag
b) the work done by the force of friction on the flight bag
c) the coefficient of kinetic friction between the flight bag and the floor
14) Two identical objects move with speeds of 5.0m/s and 25m/s. What is the ratio of their kinetic
energies?
15) Each of the following objects possesses energy. Which forms of energy are mechanical and which are
nonmechanical?
a) glowing embers in a campfire
b) a strong wind
c) a swinging pendulum
d) a person sitting on a mattress
e) a rocket being launched into space
16) What is the kinetic energy of an automobile with a mass of 1250kg graveling with a speed of 11m/s?
17) What speed would a fly with a mass of 0.55 g need in order to have the same kinetic energy as the
automobile in question 16?
19) A 2.00 kg ball is attached to a ceiling by a 1.00 m long string. The height of the room is 3.00m. What
is the gravitational potential energy of the ball relative to each of the following?
a) the ceiling
b) the floor
c) a point at the same elevation as the ball
23) A ball is thrown straight up. At what position is it’s kinetic energy at its maximum? At what position is
gravitational potential energy at its maximum?
24) Advertisements for a toy ball once stated that it would rebound to a height greater than the height from
which it was dropped. Is this possible?
25) A weight is connected to a spring that is suspended vertically from the ceiling. If the weight is
displaced downward from its equilibrium position and released, it will oscillate up and down. How many
forms of potential energy are involved? If air resistance and friction are disregarded, will the total
mechanical energy be conserved? Explain.
27) A child and sled with a combined mass of 50.0kg slide down a frictionless hill. If the sled starts from
rest and has a speed of 12.0m/s at the bottom, what is the height of the hill?
31) A 0.250 kg block on a vertical spring with a spring constant of 5.00 x 10 3 N/m is pushed downward,
compressing the spring 0.100m. When released, the block leaves the spring and travels upward vertically.
How high does it rise above the point of release?
42) When an automobile moves with constant velocity, the power developed is used to overcome the
frictional forces exerted by air and road. If the power developed in and engine is 50.0hp, what total
frictional force acts on the car at 24.6 m/s?
43) Water flows over a section of Niagara Falls at the rate of 1.2 x 10 6 kg/s and falls 50.0m. How much
power is generated by the falling water?
50) A skier of mass 70.0kg is pulled up a slope by a motor-driven cable. How much work is required to
pull the skier 60.0m up a 35º slope (assumed to be frictionless) at a constant speed of 2,0m/s?
53) Figure 5-22 on pg 197 is a graph of the gravitational potential energy and kinetic energy of a 75g yo-yo
as it moves up and down on its string. Use the graph to answer the following questions:
a) By what amount does the mechanical energy of the yo-yo decrease after 6.0s?
b) What is the speed of the yo-yo after 4.5s?
c) What is the maximum height of the yo-yo?
61) A 25kg child on a 2.0m long swing is released from rest when the swing supports make an angle of
30.0º with the vertical.
a) What is the maximum potential energy that the child has?
b) Disregarding friction, find the child’s speed at the lowest position.
c) What is the child’s total mechanical energy?
d) If the speed of the child at the lowest position is 2.00m/s, what is the mechanical energy lost due to
friction?