A cat stands on a skateboard that moves without friction along a level road at a

Question

A cat stands on a skateboard that moves without friction along a level road at a constant velocity of 2.00 m/s. She is carrying a number of books. She wishes to stop, and does so by hurling a 1.20 kg book horizontally forward at a speed of 15.0 m/s with respect to the ground. (a) What is the total mass of the cat, the skateboard, and any remaining books? (b) What mass book must she now throw at 15.0 m/s with respect to the ground to move at ?2.00 m/s?

a i got 7.18 for b?( ikeep get 1.04), but its wrong. I need help with b please

mcat+mbook)v0 =mcat(0) + mbookvbook
(mcat+1.2)(2)= 0 + (1.2)(15)
2mcat + 2.4 = 18
mcat = 15.6/2 = 7.8

Explanation / Answer

The mass of the cat and book together were moving at 2 m/s.After the book was thrown, the book moved at 15 m/s, and the cat(and all its stuff) was not moving (i.e. 0 m/s).

(mcat+mbook)v0 =mcat(0) + mbookvbook
(mcat+1.2)(2)= 0 + (1.2)(15)
2mcat + 2.4 = 18
mcat = 15.6/2 = 7.8

Now, to move at -2 m/s ...

(mcat+mbook)v0 =mcatvcat + mbookvbook
(7.8+mbook)(0) = (7.8)(-2) +mbook(15)
0 = -15.6 +15mbook
mbook = 15.6/15

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