Question

A boy weighing kilograms is riding a skateboard. He’s moving at 2 meters/second and has 40 joules of kinetic energy. He doubles his speed when he sees his friends ahead of him. His kinetic energy at the faster speed is joules.

Answer 1

Given:
K.E=40J
speed=V=2m/s 
Mass=m?

K.E=(1/2) mv²
40=(1/2 )mx 2x2
m=2x40/2x2

m=20kg

Now K.E of boay when he doubles his speed :
V=4m/s
K.e=(1/2)mv²
=1/2 x 20x 4x4
=160 J

∴K.E when he doubles his speed is 160J

Answer 2

Kinetic energy= (1/2)×mass×(velocity)^2

So mass of the object is=

(1/2) x mass x 4= 40

Or, mass= 20 kg(approx.)

Now speed is doubled,

(1/2) x m x v^2= (1/2) × 20 x 16

So the kinetic energy = 160 joules