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physics

If there were no nuclear attraction, what would be the acceleration of either of two protons released at a separation of $4 \mathrm{fm}$ ? Compare your answer with $g$ , the acceleration of gravity. (As large as your answer is, it is still small compared to nuclear accelerations)

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computer science

Consider the following code using the POSIX Pthreads API:

thread2.c
#include <pthread.h> 
#include <stdlib.h> 
#include <unistd.h> 
#include <stdio.h> 
int myglobal; 
 void *thread_function(void *arg) { 
 int i,j; 
 for ( i=0; i<20; i++ ) { 
j=myglobal;
 j=j+1; 
 printf(“.”); 
 fflush(stdout); 
 sleep(1); 
 myglobal=j; 
 }

return NULL; 
}
int main(void) { 
pthread_t mythread; 
int i; 
if ( pthread_create( &mythread, NULL, thread_function,
 NULL) ) { 
 printf(ldquo;error creating thread.”); 
 abort(); 
 } 
for ( i=0; i<20; i++) { 
 myglobal=myglobal+1; 
 printf(“o”); 
 fflush(stdout); 
 sleep(1); 
}
if ( pthread_join ( mythread, NULL ) ) { 
 printf(“error joining thread.”); 
abort();
}
printf(“\nmyglobal equals %d\n”,myglobal); 
exit(0);
}

In main() we first declare a variable called mythread, which has a type of pthread_t. This is essentially an ID for a thread. Next, the if statement creates a thread associated with mythread. The call pthread_create() returns zero on success and a nonzero value on failure. The third argument of pthread_create() is the name of a function that the new thread will execute when it starts. When this thread_function() returns, the thread terminates. Meanwhile, the main program itself defines a thread, so that there are two threads executing. The pthread_join function enables the main thread to wait until the new thread completes.

a. What does this program accomplish?

b. Here is the output from the executed program:

$ ./thread2 
..o.o.o.o.oo.o.o.o.o.o.o.o.o.o..o.o.o.o.o
myglobal equals 21

Is this the output you would expect? If not, what has gone wrong?

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physics

Is it possible for a nonzero net force to act on an object without the object's speed changing? Explain.

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biology

Treatment of a 6.0-g sample of glycogen with Tollens' $\mathrm{s}$ does reagent followed by exhaustive methylation and then hydrolysis yields $3.1 \mathrm{mmol}$ of 2,3-di- $O$ -methylglucose and $0.0031 \mathrm{mmol}$ of 1,2,3-tri- $O$ -methylgluconic acid as well as other products. (a) What fraction of glucose residues occur at $(1 \rightarrow 6)$ branch points, and what is the average number of glucose residues per branch? (b) What are the other products of the methylation-hydrolysis treatment and in what amounts are they formed? $(c)$ What is the average molecular mass of the glycogen?

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