The Student Room Group

physics question

the rollercoater car is raised to a height of 40m in 35 seconds by an electric motor
mass of rollercoaster and passengers is 550kg
motor has a power rating of 10 000 W
gravitational field strength = 9.8N/Kg

calculate the efficiency of the motor.

is the answer 1.62%???
Reply 1
What have you tried so far? How did you reach 1.62%?
Reply 2
1) mass x gfs x height
550 x 9.8 x 40 = 215600J

power = energy transferred/time
215600 / 35 = 6160

efficiency = total power output / total power input
= 10,000 / 6160 = 1.62%
Reply 3
Original post by anonymous.201
1) mass x gfs x height
550 x 9.8 x 40 = 215600J

power = energy transferred/time
215600 / 35 = 6160

efficiency = total power output / total power input
= 10,000 / 6160 = 1.62%

Agree with everything up until the last line,
When finding the efficiency you multiply by 100 at the end as you want a percentage. Meaning you would have a motor with an 162% efficiency, clearly this can't true.
The motor has 10,000W power rating, this is the power available to the motor. You've calculated how much power is used to lift the cart, 6160W. This is how much power it's using/outputting
You've got them the wrong way around in the final step.
Reply 4
Original post by Skiwi
Agree with everything up until the last line,
When finding the efficiency you multiply by 100 at the end as you want a percentage. Meaning you would have a motor with an 162% efficiency, clearly this can't true.
The motor has 10,000W power rating, this is the power available to the motor. You've calculated how much power is used to lift the cart, 6160W. This is how much power it's using/outputting
You've got them the wrong way around in the final step.


thank you so much

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