Answer:
Explanation:
We to indicate whether work is positive or negative or zero
Note, Work can be define as the produce of force and distance in the direction of the force, work is the dot product of force and displacement
W = F•d
(a) gravity acting on a falling ball
Work done acting on a falling ball is positive, since gravity does work on the ball. And g is positive downward.
Then, Work done by a free falling body is
W = mgh
(b) girl accelerating a wagon from rest
The workdone by a girl accelerating a wagon is positive
Since the wagon is a accelerating, then the velocity is increasing, then, the acceleration is positive
Work done by an accelerating car can be calculated be
W = F×d
Where the force is mass of the car times the positive acceleration
W = m•a•d
(c) a skydiver falling at terminal velocity through the air
The work done is zero since the terminal velocity is constant, so their is no change in velocity, the drag force is equal to the weight of the body and their is no external force acting on the body and the vertical acceleration goes to zero and since no acceleration, the work done is zero
W = m×a×h
W = 0J
But in this case, what is still don't by gravity. Since gravity is not zero.
(d) friction acting on a car so that it rolls to a stop.
The work done by friction is negative. This is due to the fact that the velocity of the car decreases with time and this implies that the car is decelerating, so the acceleration is negative, then,
W = m ×a × d
Since a =-ve
Then, W = —m•a•d
The work done by friction is negative
