Question

A 12-kg sled is moving at a speed of 2.0 m/s. At which of the following speeds will the sled have twice as much kinetic energy? A. 2.8 m/s B. 4.2 m/s C. 6 m/s D. none of the above

Answer 1

Answer: 2.8 m/s

Explanation:

Kinetic energy is the energy possessed by a body due to virtue of its motion - speed.

K.E. = 0.5 m v²

mass, m = 12 kg

speed, v = 2.0 m/s

K.E. = 0.5 × 12 × 2.0² = 24 J

For kinetic energy to be twice of the initial i.e. (24×2 = 48 J), the speed must be

48 J = 0.5 × 12× v'²

$v' = \sqrt{\frac {48 \times 2}{12}}\sqrt 8 = 2.8 m/s$

Thus, at speed 2.8 m/s, the sled would have twice amount of kinetic energy.

Answer 2

The answer you are looking for is A.