classical-mechanicsforcesmomentumnewtonian-mechanics
It is generally assumed, from a person's perspective, that pushing a cart is more easier than pulling one. But why?
Is there any difference in terms of force required to achieve the same amount of displacement?
Or is it merely human perception?
Why is it that almost all automobiles transfer torque to the back axle. But then, why do trains have engines in the front?
When you push a lawn mower, you are directing force down as well as forward because of the angle of the handle. This means the wheels of the mower are being pushed into the grass, which increases the rolling friction (when the wheel makes a hole in the grass, you have to "climb out of the hole" all the time; the deeper the hole, the steeper the slope you are climbing). When you pull, the force is "up and out" of the (smaller) hole - so it's easier.
A little cartoon to help:
This is ignoring the fact that most lawn mowers have a free wheel mechanism so that the blades only move when you push it forward. I don't think that's what you were asking about.
To provide a constant force of 5N you need to speed up with the block. Imagine pushing a car. Your 5N accelerates the car until it is moving at the same speed as you, so unless you speed up yourself, you can no longer apply the force. If you could, then eventually the car will be travelling faster than you and pulling away from you!
You should replace pushing the block and associated running on a friction less surface problems with a motor/fan/propeller on the block supplying the 5N force.
Best Answer
The force required to accelerate an object of a given mass by a given amount will always be constant ($F=ma$). The difference between pushing and pulling is that humans are built in a particular way - our muscles, joints and tendons won't make different actions cost the same in terms of our perceived effort, or our energy expenditure (although the useful working energy transferred to the cart will be same).
I'm not any kind of expert on human kinematics, but I expect the reason that pushing feels easier is because the point of contact (hands or shoulders) can be braced up against the cart, allowing you to use your big driving muscles (quadriceps/gluteal muscles) much more efficiently. When you pull, you've got to try to keep your arms rigid to transfer more of your driving energy into the cart - that means you're burning more energy just in your arm muscles than when you push.
As for the axle receiving the torque of a vehicular engine, I'm pretty sure it's far more to do with steering mechanics and manoeuvrability than any kind of energy transfer efficiency.