Download POP4e: Ch. 1 Problems

PHYS-2325: University Physics-I
HOMEWORK PROBLEMS
Fall-2011
Ch-8
Chapter 8: CONSERVATION OF ENERGY
Hand in your solutions in class in the lecture period after which the chapter is completed.
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
Fall-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
Fall-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
Fall-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
Fall-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.