Question

A truck starts from rest and rolls down a hill with a constant acceleration. It travels a distance of 400 m in 20 s. Find its acceleration. Find the force acting on it if its mass is 7 metric tonnes (Hint: 1 metric tonne = 1000 kg.)

  • force and laws of motion CBSE Class 9
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Answer

Initial velocity of the truck, u = 0 m/s

Time taken, t = 20 s

Distance covered by the stone, s = 400 m

According to the second equation of motion:

𝑠 = 𝑢𝑡 + 1/2 𝑎𝑡2

We have

400 = 0 × 20 +1/2 × 𝑎 × (20)2

⇒ 400 = 200𝑎

⇒ 𝑎 = 2 𝑚/𝑠2

Now, Force = mass × acceleration

⇒ 𝐹 = 7000 × 2 = 14000 𝑁

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