Question

A ball of mass 1.5kg is moving with a speed of 20m/s. Find its kinetic energy. If a force changes its speed to 25m

s-1, find the work done by this force.​

Answer 1

Given

• Initial Velocity = 20 m/s
• Mass = 1.5 kg
• Final Velocity = 25 m/s

To Find

• Initial Kinetic Energy
• Work done in changing the speed

Solution

● Kinetic Energy is given by, KE = ½mv² or ½mu²

✭ Initial Kinetic Energy

→ KE = ½mu²

→ KE = ½ × 1.5 × 20²

→ KE = ½ × 1.5 × 400

→ KE = 200 × 1.5

→ KE (Initial) = 300 J

✭ Final Kinetic Energy

→ KE = ½mv²

→ KE = ½ × 1.5 × 25²

→ KE = ½ × 1.5 × 625

→ KE (Final) = 468.75 J

✭ Work Done

→ Work = Final KE - Initial KE

→ Work = 468.75 - 300

→ Work = 168.75 J

Answer 2

Answer:

Given :-

• Mass of ball (M) = 1.5 kg =
• Initial velocity (U) = 20 m/s
• Final velocity (V) = 25 m/s

To find:-

❶ Initial kinetic energy

❷ Work done

SoluTion :-

☞ As we know that initial kinetic energy = ½ × mu²

➸ KE = ½ × 1.5 × 20²

➸ KE = 1 × 1.5 × 10 × 20

➸ KE = 300 J

➟Therefore, Initial kinetic energy = 300 Joule

☞ As we know that Final kinetic energy = ½ × mv²

➸ KE = ½ × 1.5 × 25²

➸ KE = ½ × 1.5 × 25 × 25

➸ KE = 468.75 J

➠ Therefore, Final kinetic energy = 468.75 Joule

$\sf \: total \: work = final \: KE \: - Initial \: KE$

➸ Total work = 468.75 - 300

➳ Total work = 168.75 J