Download Homework 7

Name
Period
Date
❆ ❆ ❆ ❆ Homework 7 ❆ ❆ ❆ ❆
Due 12/18Day 1 — 12/19 Day 2
1.
Under what conditions is the work done by a force negative? When is the work done by a force zero?
2.
A 0.75 kg fan cart is moving with a kinetic energy of 3.0 J and it has a potential energy of 5.0 J relative to the observer. Frictional forces
are too small to matter.
a.
_________________ How much total energy does the cart system have?
b.
_________________ If the cart reaches a position where its kinetic energy is 1.0 J, how much potential will it have?
c.
_________________ When the cart has a potential energy of 4.0 J, how fast is it moving?
d.
_________________ How much work is done by the fan on the cart when it moves from its initial to the observer’s position.
3.
A 3500 kg car speeds up from 1.5 m/s to 5.5 m/s over a time of 0.80 sec.
a.
_________________ How much net force acted on the car?
b.
_________________ How much work was done on the car?
c.
_________________ How far did the car travel in this time?
4.
A motionless cart of mass 3.0 kg (M1) is attached to a string which passes over a pulley and it tied to a mass, M2, of 1.0 kg. No other forces
acts on the cart.
a.
_________________ Calculate the weight of M2.
b.
_________________ Determine the acceleration of the cart after it is released.
c.
_________________ Calculate the tension force pulley the cart.
d.
_________________ The final kinetic energy of the cart is 4.0 J. Calculate the cart’s displacement.
e.
_________________ How much work is done on the cart through the displacement?
f.
_________________ How much gravitational potential energy did M2 have before being released?
g.
_________________ How much work does gravity to on the cart through the displacement?
e.
Sketch position-time, velocity-time, acceleration-time, and kinetic energy vs. time graphs for the cart’s motion.
Homework 7
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12/7/14
5.
a.
The force of a fan pushing a 0.33 kg cart is graphed as the cart moves from 0 to 0.5 meter. The work done by friction is negligible.
5
_________________ Calculate the work done by the fan on the cart.
c.
_________________ If the cart started from rest, how much kinetic energy will
it have at the 0.5 m position?
_________________ Calculate the velocity of the cart at the 0.5 m position.
d.
Sketch velocity-time and acceleration-time graphs to match the motion caused by
the fan force
6.
The total energy and potential energy of a system is graphed over 1.0 meter.
a.
_________________ Estimate how much kinetic energy the system has when the
position is 0.20 meter.
b.
c.
_________________ At which position(s) is the object motionless?
_________________ At which position does the object have the largest kinetic
energy?
3
2
1
0
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
10
Total Energy
5
0
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
-15
a.
_________________ Calculate the force constant (k) for this spring.
b.
_________________ Calculate the maximum speed attained by the cart after the spring is released.
A fan-drone circuit has a 5.0 voltage drop and passes 0.068 amps of current for 22 seconds. The cart has a mass of 0.44 kg.
a.
_________________ Calculate the total resistance of the circuit.
b.
_________________ Calculate electrical energy expended during the run.
c.
_________________ If the cart ended up moving 3.0 m/s, how much energy was lost to heat?
2
0.9
Potential
-10
A 0.33 kg cart is attached to a spring at its equilibrium position. 5.0 joules of work is required to compress the spring and cart to a
position 0.60 m away from the initial position.
Homework 7
0.8
-5
Position, m
8.
0.5
Position, m
-20
7.
0.45
-1
Potential, J
b.
Force, N
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12/7/14
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