Liftoff Energy
Liftoff Energy
Speed, height, and power physics help?
A 2kg toy rocket blasts straight up from the ground level with a kinetic energy of 40J. At the exact top of its trajectory its total mechanical energy is 140J. Disregard air resistance.
1. What is its speed at liftoff?
2. What maximum height does it reach?
3. If it took 30 seconds to reach the top, how much power did the engine produce after liftoff?
How do I solve these questions?
1. KE + PE = constant mechanical energy
at the top of its flight, KE=0 therefore PE = 140 J
at liftoff, PE = 0, therefore KE = 140 J
KE = 1/2 mv^2
140 J = 1/2 ( 2 kg) v^2
v^2 = 140 m^2/s^2
v= 11.83 m/s
2. max h?
PE = mgh
140 J = (2kg) (9.8 kg m/s^2) (h)
h = 7.14 m
3. P = ME / t
P = 140 J / 30 s
P = 6.47 watts
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