# Homework Help: Work and Kenitic Enegry problem

1. Mar 1, 2009

### gpr

1. The problem statement, all variables and given/known data
A 3 kg object starting at rest falls from a height of 10m to the ground. In this instance, the force of air resistance is not negligible so that the magnitude of work done by this frictional force is 20 J. What is the object's kinetic energy prior to hitting the ground?
a.78J
b.118J
c. 49J
d. 274 J

2. Relevant equations
$$KE=1/2mv^2$$
$$W=|\vec{F}||\vec{d}|cos\theta$$
W is work

2. Mar 1, 2009

### rock.freak667

Initially, the object has gravitational pe,as it falls work is done to overcome friction and the rest is kinetic energy. Can you find the kinetic energy now?