Question

On a given planet the weight of an object varies directly with the mass of an object. Suppose that an object whose mass is 3kg weighs 21N. Find the weight of an object whose mass is 7kg

Answer 1

Weight = mass*gravity
Rearrange to get gravity
Gravity = weight/mass

Using 3kg, 21N

Gravity = 21/3 = 7
On this particular planet the gravity is measure at 7 m/s

Therefore:
Weight = 7kg*7= 49N