Download POP4e: Ch. 1 Problems

PHYS-2325: University Physics-I
HOMEWORK PROBLEMS
Summer-2011
Ch-8
Chapter 8: CONSERVATION OF ENERGY
Hand in your solutions in class, on: ___________
Show the equations and calculations, and box your answer. Be sure to include the units.
NOTE: Any four questions from this HW will be graded, and the marks for this HW will be based on
these only.
1
A 2.5-kg object suspended from the ceiling by a string that has a length of 2.5 m is
released from rest with the string 40° below the horizontal position. What is the tension in the
string at the instant when the object passes through its lowest position?
2
A 0.04-kg ball is thrown from the top of a 30-m tall building (point A) at an unknown angle
above the horizontal. As shown in the figure, the ball attains a maximum height of 10 m above
the top of the building before striking the ground at point B. If air resistance is negligible, what is
the value of the kinetic energy of the ball at B minus the kinetic energy of the ball at A (K B - KA)?
3 (8.3) A bead slides without friction around a loop-the-loop. The bead is released from a height
h = 3.50R. What is its speed at point A?
PHYS-2325: University Physics-I
Summer-2011
Ch-8
4 (8.4) A particle of mass m = 5.00 kg is released from point A and slides on the frictionless track
shown in the figure. Determine the particle’s speed at points B and C and the net work done by
the gravitational force as the particle moves from A to C.
5 (8.32) A 650-kg elevator starts from rest. It moves upward for 3.00 s with constant acceleration
until it reaches its cruising speed of 1.75 m/s. What is the average power of the elevator motor
during this time interval?
6 (8.7) Two objects are connected by a light string passing over a light, frictionless pulley as
shown in Figure P8.7. The object of mass 5.00 kg is released from rest. Using the isolated system
model, determine the speed of the 3.00-kg object just as the 5.00-kg object hits the ground.
PHYS-2325: University Physics-I
Summer-2011
Ch-8
7 (8.19) The coefficient of friction between the 3.00-kg block and the surface in Figure P8.19 is
0.400. The system starts from rest. What is the speed of the 5.00-kg ball when it has fallen 1.50 m?
8 (8.21) A 5.00-kg block is set into motion up an inclined plane with an initial speed of 8.00 m/s.
The block comes to rest after traveling 3.00 m along the plane, which is inclined at an angle of
30.0° to the horizontal. For this motion, determine the coefficient of kinetic friction.
9
A 12-kg block on a horizontal frictionless surface is attached to a light spring (force
constant = 0.80 kN/m). The block is initially at rest at its equilibrium position when a force
(magnitude P = 80 N) acting parallel to the surface is applied to the block, as shown. What is the
speed of the block when it is 13 cm from its equilibrium position?
PHYS-2325: University Physics-I
Summer-2011
Ch-8
10
A 2.0-kg mass is projected from the edge of the top of a 20-m tall building with a velocity
of 24 m/s at some unknown angle above the horizontal. Disregard air resistance and assume the
ground is level. What is the kinetic energy of the mass just before it strikes the ground?
11
A 1.5-kg block sliding on a rough horizontal surface is attached to one end of a horizontal
spring (k = 200 N/m) which has its other end fixed. If this system is displaced 20 cm horizontally
from the equilibrium position and released from rest, the block first reaches the equilibrium
position with a speed of 2.0 m/s. What is the coefficient of kinetic friction between the block and
the horizontal surface on which it slides?
12
A 2.0-kg mass is projected vertically upward from ground level with an initial speed of 30
m/s. The mass rises to a maximum height of 35 m above ground level. How much work is done
on the mass by air resistance between the point of projection and the point of maximum
height?
PHYS-2325: University Physics-I
Summer-2011
Ch-8
13
The two masses in the figure are released from rest. After the 3.0-kg mass has fallen 1.5 m,
it is moving with a speed of 3.8 m/s. How much work is done during this time interval by the
frictional force on the 2.0 kg mass?
14
A champion athlete can produce one horsepower (746 W) for a short period of time. If a
70-kg athlete were to bicycle to the summit of a 500-m high mountain while expending power at
this rate, she would reach the summit in ____ seconds.