What is the weight of a 2.5 kg hammer on Jupiter, where the acceleration of gravity is 24.79 m/s^2 ?

"weight" can mean 2 things to US metric users, Force due to gravity, or just mass.
Mass = 2.5 kg, or
F = ma
F = 2.5*24.79 = 61.975, but needs 2 sigfigs: 62. N

It is not only the correct thing to do but also useful to use the units when solving these problems*.

Weight in a physical context is always a force, never just mass.
You probably know the formula F = m * a
Here, a is the "acceleration of gravity" that you are given (a is short for "acceleration" as you surely know).
All you have to do is plug in the values in the formula:
F = m * a = 2.5 kg * 24.79 m/s² = 61.975 kg m/s² ≈ 62 N**

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Alternatively, you could also point out that this is a trick question as there is no "on Jupiter" since Jupiter being a gas giant does not have a surface to be "on".  ;-)



* e.g., sometimes one can see by units alone that there's an error in  calculation
** 1 N is of course the same as 1 kg m/s²

weight Wj = m*gj = 2.5*24.79 = 62.0 N (2.5 times the weight on Earth)

In SI the weight is the force of gravity on the object 2.5 * 24.79 = 62N
However to a common man they think of weight in terms of how much force the earth exerts on a mass.  ie the hammer, on Jupiter, will have the same force as a mass of 6.3 kg would have on earth

2.5/9.81*24.79=6.32kg