To find the force that the mechanic must exert using the compound pulley, we can use the formula for mechanical advantage (MA):
\[ \text{Mechanical Advantage} = \frac{\text{Force without pulley}}{\text{Force with pulley}} \]
Given that the mechanical advantage of the pulley is 4, and the force required to lift the go-kart without the pulley is 1,620 N, we can rearrange the formula to find the force with the pulley:
\[ \text{Force with pulley} = \frac{\text{Force without pulley}}{\text{Mechanical Advantage}} \]
Substituting in the values:
\[ \text{Force with pulley} = \frac{1,620 , N}{4} = 405 , N \]
Thus, the mechanic must expend 405 N of force to lift the go-kart using the compound pulley.
The correct response is 405 N.