Question

Please help! A net force of 2.0 N acts on a 2.0-kg object for 10 seconds. What is the object’s kinetic energy after that 10 seconds (assuming the object starts from rest and there is no friction)?

Answer 1

For Newton's second law, the force F applied to the object of mass m will cause an acceleration a of the body:
$F=ma$
So, the acceleration is 
$a= \frac{F}{m}= \frac{2.0 N}{2.0 kg}=1 m/s^2$

The object undergoes through this acceleration for 10 seconds, t=10 s. Since it is an accelerated motion, we can find its final velocity after 10 seconds:
$v_f = v_i + at=0 m/s+(1m/s^2)(10 s)=10 m/s$
where $v_i$ is the initial velocity of the object, which is zero since it starts from rest.

Finally we can calculate the final kinetic energy of the object, which is given by
$K= \frac{1}{2}mv^2= \frac{1}{2}(2.0 kg)(10 m/s)^2=100 J$