Download Physics 30 Energy Go to main menu Part I (2 X 7) 1. Which of the

Physics 30
Energy
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Part I (2 X 7)
1. Which of the following are vector quantities?
I. Acceleration
II. Force
III. Momentum
IV. Work
The correct answer is
A. I and II only.
B. I and III only.
C. I, II, and III only.
D. I, II, III and IV.
2. When 6.0 kg.m/s is divided by 2.0 s, the result is equal to *****
A. 3.0 J
B. 3.0 N
C. 3.0 N.s
D. 3.0 kg.m
3. The force compression ratio of a spring is 400 N/m. The potential energy stored in the spring when compressed
0.3 m is*****
A. 18 J
B. 36 J
C. 60 J
D. 120 J
4. A 3.6 kg object is dropped from a height of 8.4 m. what is its speed when it is 2.2 m above the ground?
A. 11 m/s
B. 13 m/s
C. 26 m/s
D. 120 m/s
5. An electric motor can lift a 24 kg object vertically 15 m in 6.0 s. The power developed by the motor is *****
A. 60 W
B. 300 W
C. 588 W
D. 3528 W
6. Calculate work done in accelerating from rest a 7 Kg object 12.0 m in 3.0 s on a frictionless horizontal surface?
A. 75 J
B. 224 J
C. 252 J
D. 336 J
7. As an object falls through the air it:
I. gains kinetic energy.
II. loses kinetic energy.
III. gains gravitational potential energy.
IV. loses gravitational potential energy.
The correct responses are*****
A. I and IV.
B. I and III.
C. II and IV.
D. II and III.
Part II.
1. As shown in the diagram, a bead slides on a wire (mass 2.0 Kg). If the friction forces are negligible and the bead
has a speed of 1200 cm/s at point A (8.0 m high). (a) What is the speed at point B (ground)? (b) at point C (5.0 m)?
(5) 17.3 m/s, 14.2 m/s
2. To balls, one of mass 2 kg moving to the right at 3 m/s, the other of mass 4 kg moving to the left at 2 m/s collides
in a perfectly elastic collision. What is the speed of the balls after the collision? (5) -1.33 m/s, 3.66 m/s
3. A spring with a force constant of 4000 N/m is compressed to 0.12 m. An object of mass 2.0 kg is place in front of
the spring and released vertically, how high above the extension of the spring will the object travel (maximum
height of object)? (3) 1.5 m
(b) What is the velocity of the object just after it leaves the spring? (2) 5.4 m/s
4. A ball is rolled down a ramp as shown, How high will the ball have to be placed in order to just make it around
the loop, the loop has a radius of 5.0 m? (5) 12.5 m
5. A 4.0 kg object it pushed with a force of 30.0 N up a ramp that is inclined at 30 0 to the horizontal. The coefficient
of friction between the object and the board is 0.15. What is the efficiency of the ramp on getting work done, if the
object was pushed 0.5 m up the ramp?(5) [hint: need potential and kinetic energy at top of ramp] 83%
Answers
EI1 work is joules and has no direction
EI2 the unit is kg/m s2 this is a newton
EI3 E=0.5 kx2
EI4 conservation of energy mgh +0.5mv2=mgh you have everything but v
EI5 p=w/t and w is work that is Fd, don't forget gravity for value of a
EI6 W=Fd you must find acceleration form simple motion equation
EI7 similar to pendulum lab when an object gains kinetic energy it looses gravitational potential
energy
EII1a energy total is 300.8 J (kinetic plus potential) at point b all this is energy is kinetic
EII1b at point c all this is energy (300.8 J) is kinetic plus potential
EII2 make two equation on e with conservation of momentum the other with conservation of
energy. you will have to unknowns to solve for.
EII3a total spring energy is 28.8 J make this equal to mgh and solve for h
EII3b total spring energy is 28.8 J make this equal to 0.5mv2 and solve for v
EII4 find minimum speed for loop-to-loop (7 m/s) use mgh +0.5mv2=mgh you have everything
but h
EII5 potential energy + kinetic energy [you need velocity at top of ramp which means you need
to find the acceleration up the ramp first] , input energy 15 J (w=fd) , therefore (12.5)/15 *100
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