By conservation of momentum, we will see that the mass of Gru is 32 kilograms.
How heavy is Gru?
Here we need to use the conservation of momentum.
Initially, Gru is stop, and Agnes with a mass of 30kg has a velocity of 1.2 m/s, so the total initial momentum is:
P = 30kg*1.2m/s = 36 kg*m/s.
At the end, the total mass is M, the mass of Gru, plus the mass of Agnes:
(M + 30kg).
And the final speed is 0.5 m/s, then the final momentum is:
P' = (M + 30kg)*0.5m/s
And the final momentum must be equal to the initial momentum:
36 kg*m/s = (M + 30kg)*0.5m/s
Now we can solve that for M:
( 36 kg*m/s)/(0.5 m/s) = M + 30kg
72kg = M + 30kg
72kg - 30kg = 32 kg = M
The mass of Gru is 32 kilograms.
If you want to learn more about momentum:
https://brainly.com/question/7538238
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