Question

if a 1200 kg car accelerates from 0 m/s to 25 m/s in 8 seconds, what is the net force acting on the car?
a 75 kg hockey player is skating at 4 m/s and increases to 7 m/s over 3 seconds. what force is applied?

Explanation:

Step1: Calculate acceleration

Use the formula \(a=\frac{v - u}{t}\).
For the car: \(u = 0\space m/s\), \(v=25\space m/s\), \(t = 8\space s\). So \(a_{car}=\frac{25 - 0}{8}=\frac{25}{8}\space m/s^{2}\).
For the hockey - player: \(u = 4\space m/s\), \(v = 7\space m/s\), \(t=3\space s\). So \(a_{player}=\frac{7 - 4}{3}=1\space m/s^{2}\).

Step2: Calculate force

Use Newton's second law \(F = ma\).
For the car: \(m = 1200\space kg\), \(a=\frac{25}{8}\space m/s^{2}\). Then \(F_{car}=1200\times\frac{25}{8}\).

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For the hockey - player: \(m = 75\space kg\), \(a = 1\space m/s^{2}\). Then \(F_{player}=75\times1=75\space N\)

Answer:

The net force on the car is \(3750\space N\). The force on the hockey - player is \(75\space N\)