Question

A 10 kg block is moving along a straight line with a momentum of 80 kg-m/s. If a force of 4N acts for 10 seconds on the block opposite to the direction of initial motion of the block, then change in its kinetic energy is

Answer 1

Change in kinetic energy is 400 J

It is given that a 10 kg block is moving along a straight line with a momentum of 80 kg-m/s. If a force of 4N acts for 10 seconds on the block opposite to the direction of initial motion of the block.

then we have to find change in its kinetic energy.

linear momentum, P = mu = 80 Kgm/s

⇒10kg × u = 80 Kgm/s

⇒u = 8 m/s

we know, change in linear momentum = force × time

⇒mv - mu = 4N × 10s

⇒mv - 80 Kgm/s = 40 Kgm/s

⇒mv = 120 Kgm/s

⇒v = 12m/s

now change in kinetic energy = 1/2 mv² - 1/2 mu²

= 1/2 × 10kg × (12m/s)² - 1/2 × 10kg × (8m/s)²

= 720 kgm²/s² - 320 kgm²/s²

= 400 kgm²/s² = 400J