Kinetic energy
1.
Calculate the kinetic energy of
A a 1500 kg car moving at 20 m/s 300 000J (3 x 105J)
B a 3000 kg van moving at 10 m/s 150 000J (1.5 x105J)
C a 10 kg shell fired at 500 m/s. 1 250 000J (1.25
x 106 J)
D the 90 000 kg
space shuttle landing at 100 m/s. 450 000 000J
(4.5 x 108J)
2. You throw a ball straight up into the air.
(a) What happens to the ball’s kinetic energy as it rises? falls
(b) What is the ball’s kinetic energy at its highest point? 0
(c) What happens to the ball’s kinetic energy as it falls? increases
(d) When does the ball have maximum kinetic energy? The instant it hits the ground
3. A car, a lorry and a motor bike are travelling side by side at
25m/s. Explain which has the most kinetic energy. Lorry as it has the greatest mass
4. An empty lorry has a mass of 3 tonnes. It travels at a steady
speed of 15m/s.
(a)
Calculate the lorry’s
kinetic energy ½ x 3000 x152 = 135 000J
(b)
What would its KE be if
its mass were 6 tonnes and it still travelled at 15m/s? ½ x 3000 x152 = 270 000J (c) What will happen to the 3 tonne lorry’s kinetic energy if its
speed goes up from 15 m/s to 30m/s? ½ x 3000 x302
= 1 350 000J
5. A 800kg car travels at a steady 35m/s. Calculate its kinetic
energy. ½ x 800 x 352 = 490 000 J
6. A car has a mass of 750 kg and a velocity of 15m/s. (a)Calculate
its KE. ½ x 750 x 152 = 84375 J (b)
What is the work done by the brakes to stop the car 84375 J The brakes exert a maximum
force of 5600 N. (c) Calculate the distance travelled before the car stops. Work = F x d, so, d = work / F = 84375/ 5600 = 15m(d) Repeat this for a speed of 30m/s KE = ½ x 750 x 302 = 337 500 J Work
= F x d, so, d = work / F = 337 500/ 5600 = 60.3m
7. An air rifle pellet has a mass of 10 g. It travels at 120m/s.
(i)
Write down the pellet’s
mass in kilograms. 10/1000 = 0.01kg
(ii)
Calculate the pellet’s
kinetic energy ½ x 0.01 x 1202 = 72J
8. A football has a mass of 800 g. Its speed is10m/s. Calculate its
kinetic energy ½ x 0.8 x 102 = 40J
9. Calculate the speed that a diver will hit the water at from a 3m
board. (remember on a spring board the diver will jump up one meter before she
begins her dive)
V = √2gh = √2(9.81)(4) = √12.5
m/s