PHYS 2101

1
PHYS 2101
Spring 2009

• Work due to Spring Forces
• Power
• Work Done by Conservative Forces

2
PHYS 2101
Spring 2009
EX1
A 15.0 kg box initially sits at the bottom of a
frictionless ramp. It is pulled by a cable to
the top of the ramp, which is 2.5 m higher than
the bottom of the ramp, and brought to a stop.
How much work does each force acting on the box
do during the lift?
3
PHYS 2101
Spring 2009
EX2
A block of mass m 0.50 kg is attached to a
hanging spring and it stretches the spring by 14
cm. What is the spring constant of the spring?
4
PHYS 2101
Spring 2009
CT1
A spring with a weight attached to it bounces up
and down. As the weight reaches the bottom-most
point of its trajectory, in what directions due
the velocity and acceleration vectors
point? Velocity Acceleration 1.
4. 2. 0 5. 0 3. 6.
5
PHYS 2101
Spring 2009
CT2
Where does the spring do positive work? The
equilibrium point is at x0. (Answer all that
apply) As the block moves from 1. From xa to
x0 2. From x0 to xb 3. From xa to xb 4.
From x0 to xa 5. From xb to x0 6. From xb
to xa
x
xa
x0
xb
6
PHYS 2101
Spring 2009
EX3
A block of mass m 0.50 kg slides across a
horizontal frictionless table with a speed of v
2.0 m/s. It runs into a spring with a spring
constant k 750 N/m. What is the maximum
distance the spring is compressed?
7
PHYS 2101
Spring 2009
EX3
A 100 kg block is pulled at a constant speed of
5.0 m/s across a horizontal floor by rope with a
tension of 122 N directed 37 above the
horizontal. (a) What is the rate at which the
tension force does work on the block?
A 100 kg block is pulled at a constant speed of
5.0 m/s across a horizontal floor by rope with a
tension of 122 N directed 37 above the
horizontal. (b) What is the rate at which the
energy is added to the block?
8
PHYS 2101
Spring 2009
CT3
You need to load a heavy box from the ground onto
the back of a pickup truck. You can (A) lift it
straight up, (B) slide it up a steep, short
ramp, or (C) slide it up a long ramp. What is
the correct order for the work done by gravity in
each case? 1. WAgtWBgtWC 2. WAltWBltWC 3.
WAgtWBWC 4. WAWBWC
You need to load a heavy box from the ground onto
the back of a pickup truck. You can (A) lift it
straight up, (B) slide it up a steep, short
ramp, or (C) slide it up a long ramp. What is
the correct order for the work done by you in
each case? 1. WAgtWBgtWC 2. WAltWBltWC 3.
WAgtWBWC 4. WAWBWC
A
C
B