Ph 121 Homework 14
Problem 1
Part 1
At what speed would a 1140-kg car have the same momentum as a 12,600-kg truck traveling at 25 km/hr?
mc
1140
1140
mt
12 600
12 600
vt
15
15
vc
vt mt mc
3150
19
N
165.789
It would have to be going 166 km/hr
Part 2
The ca
Homework Solution 2
Physics 121, Section 1
Due 9/11/07
1. Wilma I. Ball walks at a constant speed of 4.83 m/s from home to the pharmacy to pick up her
prescription. She then walks back home along the same route with a constant speed of 3.66 m/s;.
What is
Homework 16
Problem 1
A rotating wheel requires a time 3.5 seconds to rotate 37 revolutions. Its angular speed at the end of the interval is f=73 rad/s.
What is the constant angular acceleration of the wheel?
f .
t.
.
.
Solve
i
2
t
12
t f
f
Out[67]=
t
Out
Homework 15
Problem 1
A car with mass mc=614 kg is initially traveling directly east with a speed vic=26.7 m/s. It crashes into the rear end of a truck
with mass mt=8710 kg moving in the same direction with speed vit=20.4 m/s. Immediately after the collis
Homework Solution 13
Physics 121, Section 1
Due 10/23/07
1. The electric motor of a model train accelerates the train from rest to 0.620 m/s in 21.0 ms. The total
mass of the train is 875 g. nd the average power in watts delivered to the train during the
Homework Solution 12
Physics 121, Section 1
Due 10/18/07
1. A particle moves under the inuence of a conservative interaction that can be represented by the
potential energy curve U(x) shown in Figure 1.
Figure 1: Potential energy curve
(a) Sketch the curv
Homework Solution 11
Physics 121, Section 1
Due 10/16/07
1. A ball with mass m = 1.72 kg is attached to a peg at point C using a length of massless string of
L = 1.54 m. It is released from the top of a vertical circle with speed v0 = 4.7 m/s as shown in
Homework Solution 10
Physics 121, Section 1
Due 10/11/07
1. The loaded car of a roller coaster has mass m = 320 kg. It goes over the top of a `hill' with a speed v
of 20 m/s. The radius of curvature R of the hill is 15 m.
(a) What are the magnitude and di
Homework Solution 9
Physics 121, Section 1
Due 10/9/07
1. A block with a mass of M = 7.65 kg is initially moving up the incline and is increasing speed with
a = 1.44 m/s2 . The applied force F is horizontal. The coecients of friction between the block and
Homework Solution 8
Physics 121, Section 1
Due 10/4/07
1. A block starts from rest at the top of a d = 2.00-m long, = 38.0 frictionless incline.
(a) What is the acceleration of the block?
Solution: Let the x direction be down the incline. The y direction
Homework Solution 7
Physics 121, Section 1
Due 10/2/07
1. (a) Why do you fall backward when standing inside a bus which is accelerating from rest?
As the bus accelerates forward, your body tends to follow Newton's First Law and not
accelerate. Thus, in an
Homework Solution 6
Physics 121, Section 1
Due 9/25/07
1. Work out the physics of the Monkey Hunter demonstration we did in class on Tuesday, September 20.
Assume that a projectile is shot from a blow gun at the same time a monkey drops from rest by letti
Homework Solution 5
Physics 121, Section 1
Due 9/20/07
1. What is wrong with the physics in the following statement? The car rounds the turn at a constant
velocity of 50 km/h Rewrite it so that it conveys the correct meaning.
Solution: If the car is round
Homework Solution 4
Physics 121, Section 1
Due 9/18/07
1. Joan measures the distance across a straight river by the following method:
Starting directly across the river from a tree on the opposite bank, she
walks 106 m along the river bank to establish a
Homework Solution 3
Physics 121, Section 1
Due 9/13/07
1. Eric slams on the brakes when he sees a tree blocking the road. The
car slows uniformly with an acceleration of -5.12 m/s2 for 3.51 s, making
straight skid marks 61.4 m long ending at the tree. Wit
Homework Solutions 1
Physics 121, Section 1
Due 9/6/07
In the rst two problems of this solution, I have included the full level of
detail I would expect to see in your solutions. In the nal problem and on
subsequent assignment, we will usually only includ