A student with a mass of 61.0 kg is walking at a leisurely pace of 1.80 m/s. What is the student's kinetic energy (in J)? _________ J A typical baseball has a mass of 0.145 kg. Some pitchers can throw a baseball with a speed of about 103 miles per hour, or about 46.0 m/s. What is the kinetic energy (in J) of a typical baseball moving at this speed?  ________J

If a particle is moving, it has kinetic energy. Kinetic energy is the energy of motion, and it depends on the speed and mass of the particle. It is given by the formula

• Kinetic energy, and every other type of energy as well, is a scalar quantity, given by only a single number. Energy does not have a "direction", unlike a vector quantity. (This is in contrast to the vector quantity momentum, which you might have already studied.)
• Kinetic energy, in particular, is always a positive number. (Note the speed v is the magnitude of the vector velocity, and therefore is positive. But even if it were a negative number, squaring it would always lead to a positive result.)
• Kinetic energy depends on the square of the speed. (This is in contrast to the magnitude of momentum, mv, a quantity you may have already studied, which depends on the speed alone.) This means that doubling a particle's speed will quadruple its kinetic energy.