Show:
Kinematics
Forces
Satellites & Gravity
Momentum
Energy
100
A squirrel crossing the road darts 0.8 m forward, 0.2 m backward, then 1.5 m forward again. What is the squirrel's displacement?
2.1 m forward
100
Draw and clearly label a free body diagram for a cart rolling along a level track. Do not ignore friction.
(Check board)
100
Most satellites orbiting the earth do so in a circular path. Which force provides the centripetal ("center-seeking") force required to hold these satellites in their orbits?
The force of gravity! For orbiting objects, the force of gravity is a centripetal force.
100
An 8 kg fish swims at 3 m/s toward a stationary 0.5 kg fishing lure and swallows it. What was the momentum of the fishing lure before the fish swallowed it?
The lure's momentum was 0 kg*m/s.
100
Consider the spheres of a Newton's cradle going back and forth. Identify one instance of energy transfer in this system.
Energy is transferred during the collisions, when one sphere exerts a force on another.
200
A squirrel crossing a 8-meter-wide road manages to make it across in 4 seconds. What is this squirrel's velocity?
2 m/s across the road
200
Suppose a little kid pushes a bowling ball down a lane. According to Newton's 1st law, in the absence of friction, what should happen to the ball after the kid stops pushing it?
The ball should keep rolling at the same speed, in the same direction. Newton's 1st Law: An object will not change its speed or direction unless it is compelled to do so by an unbalanced force. (more simply, "An object in motion stays in motion")
200
How would the force of gravity between you and the earth (that is, your weight) change if the earth had the same radius but was twice as massive?
The force of gravity on you (your weight) would double also.
200
An 8 kg fish swims at 3 m/s toward a stationary 0.5 kg fishing lure and swallows it. What was the momentum of the fish before it swallowed the lure?
The fish's momentum was 24 kg*m/s. (p= 8 kg * 3 m/s =24 kg*m/s)
200
Consider the spheres of a Newton's cradle going back and forth. Identify one instance of energy transformation in this system.
Energy is transformed from potential energy to kinetic energy as the spheres on the end fall toward the spheres in the middle.
300
Draw a velocity-time graph which correctly represents a squirrel crossing a road with a constant velocity of +3 m/s.
(Check in person)
300
A little kid pushes a 3 kg bowling ball down a lane, accelerating it at a rate of 4 m/s/s. According to Newton's 2nd law, how much force did the kid have to apply to accomplish this?
The kid must have applied 12 N of force. Newton's 2nd Law: F=ma
300
How would your mass change if the earth had the same radius but was twice as massive?
Your mass would NOT change!
300
An 8 kg fish swims at 3 m/s toward a stationary 0.5 kg fishing lure and swallows it. The law of conservation of momentum states that the total momentum of a system is constant as long as external forces like friction aren’t a factor. If momentum is conserved as the fish swallows the lure, what is the total momentum of the system after the collision?
The total momentum of the fish-lure system AFTER the collision is 24 kg*m/s, just like it was before the collision.
300
Consider the spheres of a Newton's cradle going back and forth. As the potential energy of the sphere on one end is transformed into kinetic energy, which force does the work to make this energy transformation happen?
The force of gravity!
400
Draw a position-time graph which correctly represents a squirrel crossing a road with a constant velocity of +3 m/s.
(Check in person)
400
What is the net force in the vertical direction on a bowling ball rolling down a (level) lane?
The forces are balanced - so the net force is 0 N.
400
How would the force of gravity between the moon and the earth change if the distance between them (measured from the center of the moon to the center of the earth) doubled?
The force of gravity between them would be quartered (1/4 of what it was).
400
An impulse occurs when a force acts for a certain amount of time to change momentum. If a fisherman applies a force of 5 N for 3 s to a fish on the end of the lure, what is the change in the fish's momentum?
The change in the fish's momentum is 15 kg*m/s. (I=F*t=change in p)
400
Consider the spheres of a Newton's cradle going back and forth. If the weight of one of the spheres is 0.2 N and it falls over a distance of 0.05 m (5 cm), how much work has the force of gravity done?
0.01 N*m (or 0.01 J) of work w=F*d=0.2N*0.05m=0.01 N*m
500
A squirrel (not the flying kind) is knocked unexpectedly out of a tree and undergoes projectile motion, moving in both the x-direction & the y-direction. This equation (on the board) represents its horizontal motion. What does the second number in this equation tell you?
The squirrel's initial horizontal velocity.
500
Boone Grove High School decides to build a bowling alley. A group of students determines that the lanes are not level. This (drawn on the board) is the force vector for the lane surface pushing up on a bowling ball. If we define "up" as the positive y-direction and "right" as the positive x-direction, which component of the force is larger: the x-component or the y-component?
The y-component of the force is larger.
500
The mass of the earth is 5.98*10^24 kg. The mass of the moon is 7.35*10^22 kg. The average distance between the earth and the moon (center to center) is 3.84*10^8 m. With this information, set up the equation to find (but refrain from solving for) the force of gravity between the two.
(Check)
500
A large fish swims at some velocity toward a smaller lure and swallows it. If momentum is conserved in the fish-lure collision, the fish's velocity will decrease. Explain why this would be.
The fish transfers some of its momentum to the lure, decreasing its velocity. Or, the combined mass of the fish and lure is larger than the fish on its own, so in order for momentum to remain constant the velocity of the fish must decrease (p=mv).
500
Imagine a very large Newton's cradle made of five bowling balls. Now imagine that the bowling ball on the end has a mass of 4 kg and is swung back to a height of 2 m above the other four balls. If the system doesn’t lose any energy to heat, light, sound, etc., how much kinetic energy will the bowling ball have as it strikes the other four?
The bowling ball will have ~80 J of kinetic energy. If energy is conserved (none lost because of friction), the ball should have the same amount of kinetic energy at the bottom of its motion as the amount of potential energy it had to begin with. That potential energy is PE=mgh=4kg*~10m/s/s*2m=80J.