Word problem 1
A little boy pushes a wagon with his little sister in it. The mass of his sister and wagon together is 50 kg. The wagon accelerates at 0.75 m/s2. What force is the boy pushing with?
Solution
According to Newton’s second law, Force (F) = m X a
 For the given problem, the total mass that the boy is pushing is the sum of the masses of his little sister and the wagon; which is given as 50 kg.
So, m = 50 kg and the acceleration of the wagon, a = 0.75 m/s2 Substituting these values in the formula of force, we get:
FÂ =Â 50 kg X 0.75 m/s2
=Â 37.5 kg m/s2
=Â 37.5 N
The force with which the boy is pushing the wagon is 37.5 N.
 Word problem 2
When hit by a tennis player, a tennis ball weighing 300 grams, is accelerated at a rate of 150 m/s2. What force does the player’s tennis racket exert on the ball?
Solution
In this problem, the mass of the ball is given in grams. Since the SI unit of force is kg m/s2, the mass of the ball has to be converted into kilograms.
Therefore, mass of the tennis ball, m = 300 g = 0.3 kg Acceleration a = 150 m/s2
Now substituting the values in the formula of Force (F) = m X a, we get:
F = 0.3 kg X 150 m/s2
= 45 kg m/s2
= 45 N
The force that the player’s tennis racket exerts on the ball is 45 N.
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