Show:
Energy concepts
Momentum concepts
Energy problems
Momentum problems
100
This is the standard unit of power.
Watt
100
a. What does inertia depend on? b. What does momentum depend on?
a. mass b. mass and velocity
100
What is the mass of an object with a speed of 6 m/s and a kinetic energy of 9 joules?
m = 0.5 kg
100
What is the velocity of an object that has a mass of 7 kg and a momentum of -84 kg m/s?
-12 m/s = v
200
If an object's mechanical energy goes _____________, we say that the __________ done on it was negative. (fill in the blanks)
down work
200
If an object gains mass (the mass is dropped onto it) as it slides across a frictionless surface, it will a. speed up b. continue with the same speed c. slow down d. change direction
c slow down
200
At what speed would a 250 kg grand piano hit the ground, if it were dropped from a 6 story window (18 meters)?(assuming this occurs on Earth, and that you ignore air resistance)
24.5 m/s
200
What is the impulse on a 500 kg car that was initially moving at 15 m/s and is now at rest?
-7500 N s
300
Mr. Rooney drops a 3 kg rock and a 5 kg rock from a height of 10 meters. Which of the following describes what happens? a. they hit the ground with the same speed b. the 3 kg rock will hit the ground at a greater speed c. the 5 kg rock will hit the ground at a faster speed d. Need more information to determine,
a. they will hit the ground with the same speed.
300
In an explosion, momentum is conserved. If everything started at rest, that means the total momentum before AND after is 0 kg m/s. Explain how this is possible, since after the explosion, there are moving pieces.
Since momentum is a vector, one piece can have a positive value of momentum, and the other piece a negative value of momentum, so that when you add the two together, their sum (or total momentum) is zero.
300
How long would it take to burn off a 550 calorie Big Mac if you did it by jogging at the average person jogging power-output of 500 watts? (note 1 calorie is the same as 4184 joules)
4,602 seconds = 76.7 minutes = 1.28 hours.
300
A 3 kg gun is at rest, and then fires a 0.01 kg bullet at 150 m/s. What is the recoil velocity of the gun?
-0.5 m/s
400
Mr. Rooney drops a stone form the top of a tall building. It takes 6 seconds to reach and hit the ground. 3 seconds after he dropped it, which of the following is true: a. exactly half of its energy is potential and half is kinetic b. more than half of its energy is potential and the rest is kinetic c. less than half of its energy is potential and the majority is kinetic d. all of its energy is kinetic and none of it is potential e. all of its energy is potential and none of it is kinetic.
b. more than half is potential
400
What physical quantity could be found by calculating the slope of a momentum versus time graph?
FORCE
400
A winch has a power of 1000 watts. in 1 minute, how high can it lift a 150 kg anchor? (assuming it is on Earth, and the anchor is not in the water).
40 meters
400
What is the initial velocity of a 0.25 kg snowball if the snowball hits and sticks to a 2.25 kg wooden crate initially at rest? After the snowball hits and sticks, the two move off together with a velocity of 2 m/s.
+20 m/s
500
In order to get twice the power when lifting something, you could lift three times the mass half the height in ___________ times the amount of time.
three quarters (3/4) the amount of time
500
Three balls are thrown at a glass window. The first ball bounces off the window, coming back towards the thrower. The second ball sticks to the glass. The third ball breaks the glass and goes outside. Each ball is in contact with the glass for the same amount of time. Which ball had the greatest force exerted on it by the glass? a. first ball b. second ball c. third ball d. they all experienced the same force
a. the first ball (since it bounced back, and had the greatest change in momentum.)
500
A 100kg roller coaster car is moving at 5m/s and is 60 meters above the ground when it starts down a hill. the bottom of the hill is 20 meters off the ground. Friction and air resistance do -2000J of work on the roller coaster. How fast is the roller coaster going at the bottom of the hill? (take g=10m/s^2 and round your answer to the nearest tenth.)
v = 28.0 m/s
500
Henry (59 kg) jumps off his skateboard (1 kg) when he and it are both moving at +2 m/s. Henry is going +1.8 m/s after he jumps off. What is the final velocity of the skateboard after he jumps off?
+13.8 m/s