It's about 1,000 times as heavy as a Golf Ball
In other words, 50 kilograms is 1,089 times the weight of a Golf Ball, and the weight of a Golf Ball is 0.0009183 times that amount.(per R&A USGA Rules of Golf; maximum rule weight)
According to the Rules of Golf (as approved by the United States Golf Association and the Rules Committee of the Royal and Ancient Golf Club of Saint Andrews), golf balls must weigh no more than 0.04593 kilograms. Golf balls are not required to have the familiar dimpled pattern, but the design has been popular since its invention in 1905 because it reduces drag while increasing lift.
It's about 850 times as heavy as a Tennis Ball
In other words, 50 kilograms is 867 times the weight of a Tennis Ball, and the weight of a Tennis Ball is 0.00115 times that amount.(ITF Standard; for Type 2 ball)
Per International Tennis Federation standard, regulation tennis balls must weigh about 0.0577 kilograms. Competition balls are also tested for bounce height, with the standards requiring that a ball dropped from 254 cm must bounce back to a height of 135 cm to 147 cm.
It's about 750 times as heavy as a Battery (C)
In other words, the weight of a Battery (C) is 0.0013 times 50 kilograms.(Alkaline)
A "C" size battery weighs 0.065 kilograms. C batteries are typically used in medium-drain devices such as musical instruments.
It's about 550 times as heavy as a Deck of Cards
In other words, the weight of a Deck of Cards is 0.0019 times 50 kilograms.(ISO 216 B8 size, a.k.a. "poker size" 63 x 88 mm, 52-card deck)
A deck of 52 ISO 216 B8-size playing cards weighs 0.094 kilograms. Utilizing nearly 3,700 decks, the record-holding largest card tower was built in early 2010, stood over 3.5 m (11 ft), and weighed over 272 kg.
It's about 350 times as heavy as a Battery (D)
In other words, the weight of a Battery (D) is 0.0027 times 50 kilograms.(Alkaline)
A "D" size battery weighs 0.1350 kilograms. The D size battery is the oldest of the modern battery sizes, first invented by the National Carbon Company in 1898.
It's about 350 times as heavy as a Baseball
In other words, 50 kilograms is 344.136214142250 times the weight of a Baseball, and the weight of a Baseball is 0.0029058261203125 times that amount.(MLB rules)
Per Major League Baseball rules, a baseball must weigh between 0.1417476156250 kilograms and 0.148834996406250 kilograms. A major league pitcher can throw a baseball at up to 150 kph (91 mph) (with a fastball pitch), with record-setting pitches as fast as 171 kph (106 mph).
It's about 300 times as heavy as a Billiard Ball
In other words, 50 kilograms is 306.730103909390 times the weight of a Billiard Ball, and the weight of a Billiard Ball is 0.0032601951593751 times that amount.(American-style, WPA specifications)
Per the World Pool-Billiard Association, a billiard ball weight must weigh between 0.15592237718750 kilograms and 0.170097138750 kilograms. According to legend, the difficulty in obtaining elephant ivory for the manufacture of billiard balls in the 19th century inspired the search for a replacement material, which led to the development of the first industrial plastic.