Explain why
A. a horse cannot pull a cart and run in empty space,
B. passengers are thrown forward from their seats when a speeding bus stops suddenly,
C. it is easier to pull a lawn mower than to push it,
D. a cricketer moves his hands backwards while holding a catch.
A. The Newton’s third law of motion explains that to move forward and equal and opposite reaction force is acted on the ground. If the horse pushes the ground with some force, the ground in turn exerts equal and opposite force on the feet of the horse. This reaction force is the reason for the motion of the horse. An empty space does not have a surface for friction and thus no reaction force.
Therefore, a horse cannot pull a cart and run in empty space.
B. When a speeding bus suddenly stops, the feet of the passengers are still in the contact with bus, which suddenly comes to rest. Whereas, according to Newton’s first law of motion, the upper body of the passengers which is not in contact with the bus, continues to be in motion.
As a result, the passenger’s upper body is thrown forward while the lower body comes to halt with the bus.
C. When we pull a lawn mower, a force at some angle is applied on it. The vertical component is in the upward direction. This upward component reduces the effective weight of the mower, thus making it easier to pull.
Whereas, when we push a lawn mower, a force acting at some angle is applied on it, the vertical components is in the downward direction and act thus, increases the effective weight of the land mower.
Due to the less effective weight in the first case, the land mower is easier to pull than push.
D. According to the second law of motion, we have the equation of motion as,
F = ma = 
Where
‘F’ is the force experienced by the cricketer as he catches the ball.
‘m’ is the mass of the ball
‘Δt’ is the short time of the impact with the hand of cricketer.
We can thus see from the equation that impact force is inversely proportional to the impact time, Thus, if the impact is for a shorter period of time then the force will be large.
It also shows that the force experienced by the cricketer decreases with the increase in the impact time.
Therefore, the cricketer moves his hand backward while taking a catch to increase the impact time, and hence decrease the impact force on his hand and prevent it from getting hurt.