Question

A projectile is fired at ${30}^o$ with momentum $p$. Neglecting friction, the change in kinetic energy, when it returns back to the ground, will be :

• A. $zero$
• B. $30$%
• C. $60$%
• D. $100$%

Answer 1

The correct option is A $zero$

$\text{Step 1:}$

During the projectile motion, as there is no air resistance, and only conservative gravitational force is acting, therefore the energy remains conserved.

Hence Initial total energy equals the final total energy.

$\text{Step 2:}$

When the projectile returns to the ground, it is at the same horizontal level, therefore its potential energy will be the same as initial, i.e. $\Delta U=0$

Since total energy will also be the same, hence its change in kinetic energy will also be zero i.e $\Delta K=0$.

Hence, option (A) is correct.