A ball whirled in a horizontal circle is released. An observer claims it flies radially outward. This is:

A car turns on a flat road. A student draws an FBD showing a centripetal force pointing inward AND friction pointing inward. The error is:

A mass m on a string completes a vertical circle. At the top, T = 0 (critical case). The tension at the bottom is: <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 360 210" style="max-width:360px;margin:0.5em auto;display:block;"> <title>Vertical circle — T_top=0 critical case, find T_bottom</title> <rect width="360" height="210" fill="#faf9f5" rx="8"/> <defs><marker id="ah-q06s4q3" markerWidth="8" markerHeight="6" refX="8" refY="3" orient="auto"><polygon points="0 0, 8 3, 0 6" fill="#c6613f"/></marker></defs> <circle cx="180" cy="100" r="65" fill="none" stroke="#14140f" stroke-width="1.5"/> <!-- Top --> <circle cx="180" cy="35" r="5" fill="#788c5d"/> <text x="190" y="32" font-family="sans-serif" font-size="10" fill="#788c5d">T_top = 0</text> <text x="100" y="32" font-family="sans-serif" font-size="10" fill="#14140f">v = √(gL)</text> <!-- Bottom --> <circle cx="180" cy="165" r="5" fill="#c6613f"/> <line x1="180" y1="159" x2="180" y2="120" stroke="#c6613f" stroke-width="2" marker-end="url(#ah-q06s4q3)"/> <text x="186" y="138" font-family="sans-serif" font-size="10" fill="#c6613f">T_bot = ?</text> <line x1="180" y1="170" x2="180" y2="195" stroke="#14140f" stroke-width="2" marker-end="url(#ah-q06s4q3)"/> <text x="186" y="194" font-family="sans-serif" font-size="10" fill="#14140f">mg</text> <text x="180" y="206" text-anchor="middle" font-family="sans-serif" font-size="10" fill="#14140f">T_bottom − T_top = 6mg always</text> </svg>

Three balls on strings of lengths L, 2L, 3L are whirled in horizontal circles with the same period. The ratio of centripetal accelerations a_1:a_2:a_3 is:

A student writes the centripetal acceleration as a = v/r. This is: