PHYSICS · Single correct · A Level · Physics · Mechanics and materials · Mechanics and materials
Problem
A 2.0kg cart is initially at rest on a horizontal track. A student gives the cart a single push that does 18J of positive work on the cart. The cart then travels along a rough section where friction does −6.0J of work on the cart before it compresses an ideal spring at the end of the track. At maximum compression, the cart is momentarily at rest and its center of mass has not changed height.
Which of the following equations correctly expresses energy conservation for the entire process from just before the push to maximum spring compression? (Here ΔK is the change in the cart’s kinetic energy and ΔUs is the change in the spring’s potential energy.)
(a) 18+ΔUs=0
(b) 18−6−ΔUs=0
(c) 18+6+ΔUs=0
(d) 18−6+21ΔUs=0