# Force Problem

1. Feb 14, 2008

### shenwei1988

A particle of mass m is initially moving 26.2 m/s. It is brought to rest by a constant net 542 N force in a distance of 69.2 m. Find m, the mass of the particle Assume friction can be ignored.

F=ma

the F is 542, i use V(initial)=26.2m/s and V(final)=0m/s S(distance)=69.2 to find A(acceleration). and the answer i got is a=14.886. then i use F=ma, but its wrong, anybody can help?thank you

2. Feb 15, 2008

### Dick

How did you manage to get a=14.886?? Presumably, m/s^2.

3. Feb 15, 2008

### physixguru

THIS SHOULD BE ENOUGH FOR DATA HELP:

Rate of change of momentum = force applied i.e. [m*v]/t=force
Calculate time using simple kinematic equations.. and then use the above equation....

4. Feb 15, 2008

### Dick

For the constant force case, [m*v]/t=force is m*dv/dt=force. Or F=ma. I think shenwei1988 knows that.

5. Feb 15, 2008

### shenwei1988

sorry, i am very stupid. still gOt the wrong answer.
i get 69.2/26.2=2.64=t
m*v(26.2)/2.64=F
F=54.6

6. Feb 16, 2008

### Dick

You want to use v(final)^2-v(initial)^2=2*a*s to find a.

7. Feb 16, 2008

### shenwei1988

question solved thanks a lot