Newton's Laws
Linear Motion
F=ma
Momentum
Energy
100
What is the net force on a cart that is pulled to the right with a force of 50 Newtons, while a 30 Newton frictional force acts on it.
20N
100
Cite an example of something with varying velocity and constant acceleration.
An object in freefall.
100
What is the acceleration of a 40-kg block of cement that is pulled sideways with a net force of 200N?
5 m/s^2
100
Distinguish between an elastic and an inelastic collision. For which type is momentum conserved?
elastic - bouncing; inelastic - sticking; both!
100
What is the equation for Work?
W=F x d or W=delta(KE)
200
What is the name for a quantity such as force that has both magnitude and direction?
Vector
200
Cite an example of something whose velocity and acceleration are in opposite directions.
Something slowing down.
200
What is the mass of an object that weighs 35 N?
3.5kg
200
What are the two ways to increase impulse?
Increase force and time.
200
How does the useful work output of a machine and its total energy input relate to its efficiency?
efficiency = work output / total energy input
300
What is the net force on an object that has reached terminal velocity?
0
300
A ball rolls from rest down an inclined plane. Its velocity after 1 second is 3m/s. What is its velocity after 2 seconds?
6m/s
300
A 3kg rock is thrown straight up at 43 m/s. It undergoes free fall, eventually reaching its original height, where it is caught. What is the force on the rock while it is in the air?
30N
300
A 1,000kg car with a speed of 30 m/s collides head-on with a 1,500kg truck going 20 m/s. What is the momentum of the system before they collide?
0 kg m/sec
300
How much work is required to change the velocity of a 500kg car from 20 m/s to 30 m/s?
Work = delta (KE) = KE (final) - KE (initial) = .5*500(30)^2-.5*500(20)^2 =125,000J
400
What is the test for whether a moving object is in equilibrium?
-constant velocity (straight line)
400
An object has an acceleration of 5m/s^2. If it starts from rest, how fast is it going after 3 seconds?
15 m/s
400
What is the acceleration of a 20-kg pail that is pulled upwards with a force of 400N?
10m/s^2
400
A car crashes into a wall at 25m/s and is brought to rest in 0.1s. Calculate the average force exerted on a 1kg test dummy by the seat belt.
250N
400
An electric motor lifts an elevator 10.00 m in 15.0 s by exerting an upward force of 15,000 N. What power does the motor produce?
P = Work / time = 10,000 Watts
500
Ms. Remus sets her niece Katy in motion across a frozen pond using a 10N push. If ice friction and air resistance are neglected, how much force is required to keep Katy sliding at constant velocity?
0 N
500
An apple falls from a tree and hits the ground after 1 second. What was its initial height?
5 m.
500
To do a physics experiment, a woman weighing 560N steps on a scale in an elevator at the bottom floor. She hits the up button and the scale jumps to 568N for 1.43 sec. What is the acceleration of the elevator?
Net Force = 568-560 = 8N Mass = 560/10=56 kg acc = F/m = 8/56 = 1/7 m/s^2 = .14m/s^2
500
A 1,000kg car moving east with a speed of 40 m/s collides head-on with a 1,500kg truck going west at 20 m/s. The car and truck stick. What is the speed and direction of the combined mass of metal?
p = 40,000-30,000 = 10,000 east v=p/(m1+,2)=10,000/2,500 = 4 m/s east
500
You decide to go to Six Flags this summer and ride a roller coaster. The coaster has a mass of 200 kg. The top of the first hill is 62 m and the top of the second hill is 44 m. Ignore friction and assume the coaster starts from rest at the top of the first hill. How much kinetic energy do you have at the top of the second hill?
TE = PE(initial) = mgh = 200*10*62 = 124,000kgm^2/s^2 KE(2nd) = TE - PE(2nd) = 124,000 - 200*10*44 = 36,000J
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