Phys 135 A
Hw 8
Note: These problems are from Giancoli 6th Edition Chapter 6 and 7.
Chapter 6:
1-P58- (I) How long will it take a 1750-W motor to lift a 315-kg piano to a sixth-story
window 16.0 m above?
2- P62- (II) Electric energy units are often expressed in the form of “kilowatt-hours.” (a)
Show that one kilowatt-hour (kWh) is equal to
J. 106.3
6
×
(b) If a typical family of
four uses electric energy at an average rate of 520 W, how many kWh would their
electric bill be for one month, and (c) how many joules would this be? (d) At a cost
of $0.12 per kWh, what would their monthly bill be in dollars? Does the monthly
bill depend on the rate at which they use the electric energy?
Chapter 7:
3-P4- (II) A child in a boat throws a 6.40-kg package out horizontally with a speed of
,sm 0.10
Fig. 7–31. Calculate the velocity of the boat immediately after, assuming it
was initially at rest. The mass of the child is 26.0 kg, and that of the boat is 45.0 kg.
Ignore water resistance.
4- P17-(II) A tennis ball of mass
kg 060.0=m
and speed
sm 25=v
strikes a wall at a 45º
angle and rebounds with the same speed at 45º (Fig. 7–32). What is the impulse
(magnitude and direction) given to the ball?
5- P34 (II) An internal explosion breaks an object, initially at rest, into two pieces, one of
which has 1.5 times the mass of the other. If 7500 J were released in the
explosion, how much kinetic energy did each piece acquire?
6- A billiard ball with mass 3 kg moves to the right with 4 m/s. It then collides head-on
with another billiard ball with mass 1 kg that was moving to the left with 2 m/s.
Determine the speed of the balls after the collision.