Question

An open cart on a level surface is rolling without frictional loss through a vertical downpour of rain, as shown. As the cart rolls, an appreciable amount of rainwater accumulates in the cart. The speed of the cart will 

(A) increase because of conservation of momentum 

(B) increase because of conservation of mechanical energy 

(C) decrease because of conservation of momentum 

(D) decrease because of conservation of mechanical energy 

(E) remain the same because the raindrops are falling perpendicular to the direction of the cart's motion

Answer 1

Correct option (C) decrease because of conservation of momentum

As the cart moves forward it gains mass due to the rain but in the x direction the rain does not provide any impulse to speed up the car so its speed must decrease to conserve momentum