Question
Why does a horse need to apply more force to start a horse cart than to keep it moving?
Solution
When the horse cart is stationary, the muscular force provided by the horse is used to overcome the static friction as well as to provide acceleration to the cart.
As the cart begins to move, the friction becomes lesser since it is rolling friction and the muscular force of the horse is utilised to only overcome this friction.
Hence, initiailly to set the cart in motion, the horse needs to do more work than, when the cart is in motion.
