Fundamental Interactions
The equation for electric force is?
1/4pi epsilon0 q1q2/|r|2 rhat
Impulse is defined as...
Fnetdt is the amount of interaction affecting the object.
A professors hand is located at +1.5 m and moves to -2.0 m. What is the displacement of the professors hand relative to the starting position of her hand?
Fon 1 by 2=-Fon 2 by 1
Which of the following is conserved when two balls at the same temperature collide?
(a) Charge
(b) Mass
(c) Momentum
(d) Energy
Conservation of momentum or energy.
What can be used to calculate the direction of gravitational force? (HINT: Think in terms of variables)
-rhat
A skydiver jumps out of an airplane and her parachute opens. At a particular instant, the upward air resistance force is equal to the downward force of gravity. Which of the following is true?
A. She will float without moving up or down.
B. She will fall faster and faster.
C. She will fall at a constant speed.
C. She will fall at a constant speed.
Jill sets out from her home to deliver flyers for her yard sale, traveling due east along her street lined with houses. At 0.5 km and 9 minutes later she runs out of flyers and has to retrace her steps back to her house to get more. This takes an additional 9 minutes. After picking up more flyers, she sets out again on the same path, continuing where she left off, and ends up 1.0 km from her house. This third leg of her trip takes 15 minutes. At this point she turns back toward her house, heading west. After 1.75 km and 25 minutes she stops to rest. What is her average velocity over the whole trip?
vavg=total displacment/elapsed time
vavg=-0.75 km/58 min=-0.013 km/min
A 60 kg person stands on Earth's surface.
(a) What is the approximate magnitude of gravitational force on the person by the Earth?
(b) What is the magnitude of gravitational force on the Earth by the person?
(60kg)9.8ms=588N
(60kg)9.8ms=588N
A car with mass m1 and initial velocity v1 strikes a car of mass m2, which is at rest. If the two cars stick together after the collision, what is the final velocity?
p1=p2
p=mv
p1=m1v1+m2v2
p1=m1v1+m2(0m/s)=m1v1
p2=m1v3+m2v3
p2=v3(m1+m2)
p1=p2
m1v1=v3(m1+m2)
m1v1/m1+m2=v3
Why is the equation Fg=mg a good approximation of gravitational force near Earth's surface?
Because the distance to earths surface is significantly smaller than the radius of Earth.
You give a toy car a push. Why does it continue to roll away from you after your hand is no longer touching it?
The momentum of the car just after it leaves your hand reflects the total impulse given to the car by your hand.
A boy who has an initial velocity of 2 m/s had already covered a distance of 10 m. If it has a constant acceleration of 2 m/s2, find the position of the boy at the end of 5s.
x(t)=½at2 + v0t + X0
(½ x 2 x 25) + (2 x 5) + 10 = 45m
A bird flies by using its wings. Using the definition of reciprocity, describe how a bird stays in flight.
A birds wings pushing air down generates and upward force equal and opposite to the force of gravity pulling the bird down.
Hockey puck A (2kg) travels with a velocity of 40ms to the right when it collides with hockey puck B (1.6kg), which was originally at rest. After the collision, puck A is stationary. Assume no external forces are in play and that the momentum of the pucks are conserved. What is the final velocity of puck B after the collision?
m1v1i = m1v1f + m2v2f
2(40m/s)=1.6v2f
80=1.6v2f
80/1.6=v2f
v2f=50ms
The moon's distance from the center of the Earth was decreased by a multiple of three. How would this affect the gravitational force of the Earth on the moon?
It would increase by a factor of nine
F1=(Gm1m2)/r2 -> F2 = (Gm1m2)/(1/3r2) = 9F1
If a 5-kg bowling ball is projected upward with a velocity of 2.0 m/s, then what is the recoil velocity of the Earth (mass = 6.0 x 1024 kg).
p=5kg * 2.0 m/s
v = (10 kg*m/s)/(6*1024 kg)
v = 1.67*10-24 m/s (downward)
A person travels 30m distance. Calculate the position of the person at the end time 6s if the initial velocity of the person is 4m/s and angular acceleration is 3 m/s2.
X(6) = 0.5 × 3 × (6)2+ 4 × 6 + 30
X(6) = 54 + 24 + 30
X(6)= 108 m
A cat of mass 5kg jumps on a dining table of mass 30kg. As the cat walks around on the table, what is the average force that the table applies to the cat?
Fg=F N=ma=5(kg)(9.8m/s2)~50N
A 3000-kg truck moving with a velocity of 10 m/s hits a 1000-kg parked car. The impact causes the 1000-kg car to be set in motion at 15 m/s. Assuming that momentum is conserved during the collision, determine the velocity of the truck immediately after the collision.
3000 * v +15000 = 30000
3000*v = 15000
v=5.0m/s
There are two point charges in a vacuum, −4μC and 5μC, kept 2m from each other. What is the force experienced by the charges?
F=k (q1q2)/r2
F=(9e9(-4e-6 x 5e-6))/22
F=-0.045 N
Force is negative because it is attractive.
A tennis ball travelling in the -x direction with magnitude of momentum 2.8 kg*m/s hits a wall and rebounds. After the collision the balls momentum is nearly the same but traveling in the +x direction. What is impulse applied to the ball by the wall?
(<2.8, 0, 0>kg*m/s - <-2.8, 0, 0>kg*m/s)=Fnetdt
<5.6, 0, 0>kg*m/s = Fnetdt
A soccer ball, whose mass is 0.45 kg is initially at rest on the surface of the moon at location <0,0,0>m. On the surface of the Moon, the constant g~1.6N/kg. An astronaut kiche ball giving it an initial velocity of <15, 15, 0>m/s. What are the coordinates of the highest position the ball reaches?
vyf=vyi+((-mg)/m)t
0=15 m/s + (-1.6N/kg)t
t=9.365s
yf=yi + vyt + 1/2((-mg)/m)t2
yf=0 + (15 m/s)(9.375s) + (0.5)(-1.6N/kg)(9.375 s)2
yf=70.3 m
xf=xi+vxit
xf=0+(15 m/s)(9.375 s)
xf=140.6
<140.6, 70.3, 0>m
A 15 kg block and a 10 kg block are hanging on opposite sides of a pulley (see picture). Assuming a frictionless, massless pulley, determine the acceleration of the blocks once they are released from rest. (Assume g~10 m/s2)
Each block is Fg=mg
Using Fnet=ma
150 N - T + T - 100 N = ma
150 N - T + T - 100 N =25 kg * a
a = 50 N/25 kg = 2.0 m/s2
Two bumper cars at an amusement park collide as one approaches the other directly from the rear. The car in front (CarA) has a mass of 550kg and the car behind it (CarB) has a mass of 450kg. The car in front was traveling at 3.70m/s while the car behind hit him with a velocity of 4.50m/s. What are their final velocities after the collision?
vBf=3.6 m/s
vAf=4.4 m/s
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