A 0.50kg cart is pushed up a rough ramp. At the bottom (point P) its speed is 3ms−1. It comes momentarily to rest at the highest point (point Q) and then rolls back down, reaching 2ms−1 at point R near the bottom. A student draws separate energy-bar charts for points P, Q, and R, using the cart–Earth–ramp surface as the system. The only permitted bars are kinetic energy (KE), gravitational potential energy (PEg), and thermal energy (Eth).
Which statement about the relative heights of the thermal-energy bars is most consistent with energy conservation?
a) The thermal-energy bars are equal in height at Q and R, and zero at P.
b) The thermal-energy bar is tallest at Q, shorter (but non-zero) at R, and zero at P.
c) The thermal-energy bar is tallest at R, shorter (but non-zero) at Q, and zero at P.
d) Thermal-energy bars are zero at all three points.