Problem 11.10

For this problem use the equation

torque=(moment of inertia) * (angular acceleration).

So you need the moment of inertia I.

You have to use

I=(1/12) ML^2 where M is the mass of the ladder and L is the length.

This is the formula for the moment of inertia of a rod around an axis at its center.

Problem 11.9

Use the formula that

torque = moment of inertia * angular acceleration

Find angular acceleration from the information given: (430 rev/min and 2 revs).

For moment of inertia use the formula for I for a disk.

11.46

For this problem let the axis of rotation be the end of the stick where the paint can is hanging.
Also, assume the whole mass M acts as if at the center of that Mass i.e. 0.5 m away from the
axis of rotation.

Problem 9.15

The impulse is the change in momentum. So compute the vector
J= m*vf - m*vi then compute the angle. Note the angle is pointing towards
the top left quadrant so your angle to the x-axis should be larger than 90.

Problem 9.28

First review your notes. I did a problem very similar to this in class. There
are two steps.

1. First apply conservation of momentum to find the velocity of the putty block system.
2. Then apply conservation of total energy to find the height the putty+block will go.

Problem 9.20

Use conservation of momentum. The initial momentum is zero. Solve for final
momentum of the astronaut. Use this to find velocity and then distance (d=v*t).

Problem 6.28

The key to this problem is to note that the tension T is the same for all segments of the rope.
Once you know this, simply draw the forces acting on the two pulleys. For example the lower pullley will feel a force 2T due to the two segments of rope pulling it UP, it will also feel a
force mg pulling it down. The net force will yield the acceleration of the box.

Problem 5.32

Before you do this problem review the elevator problem. There, the key idea is to write the equation for the forces acting on the person on the elevator:

N-W=ma

where N is the normal force: the force the scale is exerting on the person, and where a is the acceleration of the person. The scale "reads" the force exerted on it which is the normal force N.

So for the person on the boat you have 3 force measurements. One is when the boat is stationary, which should give you the persons weight, and therefore mass. The maximum force measurement (220 lb) should give you max acceleration etc. make sure you convert lb to Newtons.

Problem 5.20

First draw the figure and think of the forces acting on the surfer.
The weight of the surfer is acting straight down, the normal force of the wave
on the surfer is perpendicular to the direction of motion.

Choose the x-axis as the plane the surfer is moving in. Apply Newton's second law along this direction.

Problem 3.28

To input the unit vector simply click on the left most button right above the equation. Then click on the button with a box and ^ symbol on top.

Problem 2.53

For part D.

The key is to break the motion into two parts. The first part is during the reaction time. In this time the car moves at constant velocity (it has not began decelerating yet). The second part of the motion is when the person steps on the brakes. In this case you have a constant negative acceleration until the car stops.

Find the distance traveled during each segment and the sum should add to the given 55m.

Label the reaction time with a variable T, and then solve for T in the above equation.

Problem 2.22

Part C asks for AVERAGE SPEED.

Hint: Average speed = total distance traveled/time elapsed.
So you have to look at the graph and estimate the total distance traveled in the given time
in the one second interval.

Problem 2.60

Before you do this problem make sure to go over the cop/speeder problem that we did in class.

The only difference here is that the bicycle which passes the stationary bicycle moves an EXTA 2 seconds. So you have to account for this extra 2 seconds in the equation for distance traveled.

Your final equation will be a quadratic equation, which you should be able to solve.

Problem 2.22

For this problem you have to plot the graph for ALL tick marks along the t-axis.
This is a total of 11 points. So just calculate x vs t at each interval.

Problem 1.39B

The problem gives the number of wing beats in one second. Using this, find the the time it takes for one wing beat. Similarly, given that there are 9,192,631,770 cesium-133 oscillations in one second, find the time for one oscillation. The number of cesium oscillations that occur during one wing beat is just: time for one wing beat/ time for one cesium oscillation.

Physics 100a

In the first part of the class, we will try to understand the laws of motion. All questions on the homework will be discussed on this blog.

This blog is for physics 100a at CSUN!