Question

john coasts on his skateboard at a speed of 2 m/s. he uses his foot to increase his speed to 5 m/s. if he has a mass of 80 kg, what impulse did he apply?

a. 400 kg·m/s
b. 160 kg·m/s
c. 240 kg·m/s
d. 320 kg·m/s

Explanation:

Step1: Recall impulse - momentum theorem

Impulse $J=\Delta p = m\Delta v$.

Step2: Calculate the change in velocity

$\Delta v=v_f - v_i$, where $v_f = 5\ m/s$ and $v_i = 2\ m/s$. So $\Delta v=5 - 2=3\ m/s$.

Step3: Calculate the impulse

$m = 80\ kg$, and $J=m\Delta v$. Substitute the values: $J=80\times3 = 240\ kg\cdot m/s$.

Answer:

C. $240\ kg\cdot m/s$