Work Energy and...

A car is moving at $$100\ km/h$$. If the mass of the car is $$950\ kg$$, Its kinetic energy is:

A girl weighing 50 kg makes a high jump of 1.2 m.What is her kinetic energy at the highest point? $${(g= 10 ms^{-2}}$$)

A rifle bullet loses 1/20th of its velocity in passing through a plank. Assuming constant resistive force, the least number of such planks required just to stop the bullet is : 

The moon revolves around the earth because the earth exerts a radial force on the moon. Does  the earth perform work on the moon?

A ball moving with a velocity v strikes a wall moving toward the ball with a velocity u. An elastic impact lasts for t sec. Then the mean elastic force acting on the ball is 

Asha lifts a doll from the floor and places it on a table. If the weight of the doll is known, what else does one need to know in order to calculate the work Asha has done on the doll?

A man throws the brick to the height of 12 m where they reach with a speed of 12 m/s. If he throws the bricks such that they just reach this height, then what percentage of energy will be save?

Two bullets P and Q, masses 10 and 20 g, are moving in the same direction towards a target with velocities of 20 and 10 m/s respectively. Which one of the bullets will pierce a greater distance through the target?

The relationship between force and position is shown in the figure (in one dimensional case). Work done by the force in displacing a body from 

A body rolling down a hill has :