Newton's Laws
What is the net force on an object in equilibrium?
0
Does it require more force to start pushing a car or to keep it moving? Why?
Start pushing
The total momentum of two cars about to collide is 3000 kg m/s. The two cars stick together after the collision. What is the momentum of the stuck-together-cars after the collision?
3000 kg m/s
What is the kinetic energy of a 55-kilogram skier traveling at 11.0 meters per second?
3327.5 J
A horizontal force of 20 Newtons eastward causes a 10-kilogram box to have a displacement of 8 meters eastward. The total work done on the box by the 20-Newton force is
160 N
A student pulls a 60-Newton sled with a force having a magnitude of 20 Newtons. What is the magnitude of the force that the sled exerts on the student?
20 N
Newton's Third Law.
A 15 kilogram cart moves in a horizontal circular path of 1.3 meter radius at a constant speed of 2 meters per second.
Calculate the magnitude of the centripetal force on the cart.
46N
Change in momentum
Unit is kg m/s
A block slides across a rough, horizontal tabletop. As the block comes to rest, what type of energy is increasing?
Internal Energy (heat)
A motor does a total of 480 Joules of work in 10.0 seconds to lift a 12-kilogram block to the top of a ramp. The average power developed by the motor is
40 W
What is the weight of a 65 kg person?
638 N
What is the force necessary to keep a 5 kg steel block moving at a constant velocity of 3 m/s upon a flat steel table?
28N
A 0.06 kg ball traveling at 60.0 meters per second hits a concrete wall. What speed must a 0.02 kg bullet have in order to hit the wall with the same magnitude of momentum as the ball
180 m/s
p = mv
After a 65-Newton weight has fallen freely from rest a vertical distance of 8.0 meters, the kinetic energy of the weight is
520 J
Which unit is equivalent to a Newton per Kilogram?
a) m/s^2
b) W/m
c) kg m/s
d) J s
m/s^2
Newton's second law tells us that a = F/m
What is one way you could (realistically) quadruple the force of gravity attracting two people together.
Halve the distance.
What is the velocity of an ball tied to a 3m rope and swung around so it completes 6 revolutions in 30 seconds?
3.8 m/s
Why doesn't an egg break when thrown at a pillow, when it does break when thrown at a wall? (Be as specific as possible, using physics concepts.)
Impulse theory tells us that J = F*t = delta p
Force x time = change in momentum
The longer it takes something to change its momentum, the less the force it feels.
(see accompanying diagram
Keanu Reeves is driving an 8000 kg bus traveling on a straight road which rises and falls. The speed of the bus at point A is 27 m/s. The engine has been disengaged and the bus is coasting.
But wait! A villain has planted a bomb on the bus! If the speed of the bus falls below 22 m/s, the bomb will explode!! Will the speed of the bus fall below this value and explode? Explain your reasoning and show all calculations.
Won't explode. Lowest velocity will be 23m/s
A motor does 20 Joules of work on a block, accelerating the block vertically upward. Neglecting friction, if the gravitational potential energy of the block increases by 12 Joules, what happed to its kinetic energy?
Increased by 8 J
What force is required to lift a 20 kg concrete block upwards with an acceleration of 3 m/s2?
260 N
A woman is pulling a 10 kg cart with a force of 20N at a 30 degree angle with respect to the horizontal. The cart moves at a constant horizontal velocity. What is the coefficient of kinetic friction in this circumstance?
Around 0.18
The net force in the x-direction is 0 (because constant velocity). So the applied force should equal the frictional force. Solve for u.
A 100 kg ice skater moving at 2 m/s to the east sees their long thought dead, 75 kg old skating partner skating towards them at 3 m/s to the west. After the two skaters collide, the embrace each other in a long hug. With what speed do the two re-united skaters move and in what direction?
0.14 m/s to the west
A 0.05kg spring toy which is compressed 4 cm reaches a maximum height of 0.3 meters when launched. What is the spring constant of the toy?
184 N/m
Calculate the force Superman needs to bring this 6.5 x 103 kg train car to rest from an initial speed of 40 m/s over a distance of 70 meters.
7.4 x 10^4 N